THE  ELECTRIC  RAILWAY 


McGraw-Hill  DookCompany 


Electrical  World         The  Engineering  and  Mining  Journal 
Engineering  Record  Engineering  News 

Railway  Age  Gazette  American  Machinist 

Signal  E,ngin<?<?r  American  Engineer 

Electric  Railway  Journal  Coal  Age 

Metallurgical  and  Chem  ical  Engineering  P  o  we  r 


THE 

ELECTRIC  RAILWAY 


BY 
A.  MORRIS  BUCK,  M.E. 

ASSISTANT  PROFESSOR  OF  RAILWAY  ELECTRICAL  ENGINEERING 
UNIVERSITY  OF  ILLINOIS. 


FIRST  EDITION 


McGRAW-HILL  BOOK  COMPANY,  INC. 

239  WEST  39TH  STREET,  NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.  C. 

1915 


COPYRIGHT  1915,  BY  THE 
McGRAW-HiLL  BOOK  COMPANY,  INC. 


THE    MAPLK     F  H  E  S  S     YORK     PA 


PREFACE 

For  several  years  the  author  has  felt  the  need  of  an  adequate 
text-book  for  instruction  of  advanced  students  taking  electric 
railway  courses.  It  was  to  meet  this  need  that  this  volume  was 
prepared.  It  is  so  arranged  that  certain  portions  may  be  omitted 
without  affecting  the  continuity,  as  each  chapter  is  a  complete 
unit  in  itself. 

Since  most  students  take  electric  railway  courses  after  having 
mechanics,  a  fundamental  knowledge  of  this  subject  is  assumed. 
Similarly,  power  plant  and  transmission  line  work  are  usually 
taken  as  independent  courses,  and  are  referred  to  in  this  book 
only  as  they  directly  affect  the  main  subject.  Car  house  design 
and  equipment  are  entirely  omitted,  for,  while  of  prime  impor- 
tance in  electric  railway  operation,  they  are  topics  of  limited 
scope  which  have  no  direct  bearing  on  the  other  factors  which 
make  up  a  railway  system.  Such  points  are  very  fully  covered 
in  some  of  the  recent  electrical  handbooks. 

Although  intended  primarily  as  a  text-book,  it  is  believed  that 
this  volume  contains  much  matter  of  interest  to  the  practising 
engineer,  since  it  purposes  to  give  the  underlying  principles  of 
electric  railway  design  and  operation.  It  must,  however,  be 
borne  in  mind  that  no  attempt  has  been  made  to  write  a  hand- 
book, and  that  definite  figures  have  been  given  only  when  neces- 
sary to  make  the  text  clear. 

In  connection  with  a  book  of  this  character,  the  author  con- 
siders it  essential  that  frequent  reference  be  made  to  the  current 
technical  press  for  standard  practice  and  recent  developments  in 
the  field.  The  Electric  Railway  Journal  is  especially  to  be  recom- 
mended in  this  connection. 

It  is  impossible  to  give  credit  for  all  the  suggestions  and  criti- 
cisms which  have  aided  the  author  in  the  preparation  of  this 
book.  The  sources  of  material  are  given,  so  far  as  possible,  in 
footnotes.  Especial  thanks  are  due  Prof.  A.  S.  Richey,  of  Wor- 
cester Polytechnic  Institute,  for  reading  the  manuscript,  and  for 
valuable  suggestions  made  by  him;  and  Mr.  E.  G.  Young,  of  the 
University  of  Illinois,  for  his  aid  in  preparing  the  illustrations. 

URBANA,  ILLINOIS,  A.   M.  B. 

August,  1915. 


313776 


CONTENTS 

PREFACE    v 

CHAPTER  I 

PAGE 

INTRODUCTION 1 

The  Requirements  of  Transportation — The  Trunk  Line  Railroad — 
The  Street  Railway — The  Cable  Railway — The  Electric  Street 
Railway — The  Interurban  Railway — Scope  of  the  Electric  Railway 
— Classification  of  Railways — Motive  Powers — The  Steam  Loco- 
motive— Other  Motive  Powers — Electric  Systems — Advantages 
of  Electric  Systems — The  Railway  Problem. 

CHAPTER  II 

THE  MECHANICS  OF  TRACTION 12 

Fundamental  Principles — Work  and  Energy — Acceleration — 
Rotational  Acceleration — Total  Accelerating  Force — Train  Resist- 
ance— Journal  Friction — Flange  Friction,  Rolling  and  Oscillatory 
Resistances — Air  Resistance — Motor  and  Gearing  Friction — 
Determination  of  Train  Resistance — Train  Resistance  Formulae — 
Incidental  Resistances — Grades — Virtual  Grades — The  Ruling 
Grade — Curves — Wind  Resistance — The  Speed- Time  Curve — 
Components  of  the  Speed-Time  Curve — Acceleration  Curve — 
Coasting  Curve — Braking  Curve — Calculation  of  Speed-Time 
Curves — Total  Force  for  Train  Operation — Plotting  Speed-Time 
Curves — Power  for  Train  Movement. 

CHAPTER  III 

MOTORS  FOR  TRACTION , 42 

Functions  of  Motor  Powers — Electric  Distribution  Systems — Classi- 
fication of  Electric  Motors — Torque  Characteristics — Speed 
Characteristics — The  Direct-Current  Series  Motor — Variation  of 
Speed  Characteristic — Variation  of  Speed  with  Resistance — Torque 
Characteristic — Variation  of  Field  Strength — Losses  in  the  Series 
Motor — Efficiency  of  the  Series  Motor — Alternating-Current 
Commutator  Motors — Frequencies  of  Single-Phase  Motors — 
Variations  of  the  Alternating-Current  Series  Motor — Repulsion 
Motor — Compensated  Repulsion  Motor — Performance  of  the 
Alternating-Current  Series  Motor — Variation  of  Single-Phase 
Motor  Characteristics — Commutation  in  Single-Phase  Motors — 
The  Polyphase  Induction  Motor — Induction  Motor  Performance. 

vii 


viii  CONTENTS 

CHAPTER  IV 

PAGE 

RAILWAY  MOTOR  CONSTRUCTION 71 

Motor  Development — Early  Motors — Armature  Construction — 
Armature  Speeds — Field  Frames — Modern  Direct-Current  Rail- 
way Motors — Modern  Motor  Frames — Use  of  Interpoles — Modern 
Armature  Construction — Commutator  Construction — Motor  Lu- 
brication— Bearing  Housings  and  Bearings — Ventilation  of  Motors 
— Single- Phase  Commutator  Motors — Induction  Motors. 

CHAPTER  V 

CONTROL  OF  RAILWAY  MOTORS 84 

Need  for  Control — Available  Methods — Change  of  Potential — 
Methods  of  Potential  Variation — Changes  in  Armature  and  Field 
Strength — Changes  in  Number  of  Poles,  and  in  Frequency — Prac- 
tical Combinations  of  Control  Methods — Rheostatic  Control — 
Limitations  of  Rheostatic  Control — Series-Parallel  Control — Type 
K  Controllers — Type  L  Controller — Multiple-Unit  Control — 
Sprague  System — Type  M  Control — Unit  Switch  Control — Bridge 
Connection — Pneumatically  Operated  Drum  Control — Jones  Type 
Control — Proportioning  of  Resistances — Graphical  Method  of 
Calculating  Resistances — Time  for  Operating  Controller — Resist- 
ors for  Railway  Service — Control  of  Single-Phase  Motors — Com- 
bination Systems  for  Single  Phase  and  Direct  Current — Control  of 
Three-Phase  Motors — Changes  in  Number  of  Poles — Changes  in 
Frequency — Concatenation  of  Induction  Motors — Split-Phase 
Control — Special  Systems — Ward-Leonard  System — Permutator 
Control — Mechanical  Rectifier — Mercury  Vapor  Rectifier. 

CHAPTER  VI 

POWER  REQUIREMENTS  AND  ENERGY  CONSUMPTION 127 

Requirements  of  Train  Operation — "Straight  Line"  Speed-Time 
Curves — Speed- Time  Curves  with  Electric  Motors — Current- 
Time  Curves — Power- Time  Curves — Use  of  the  Current  and 
Power  Curves — Motor  Capacity — Heating  Limits — Character  of 
Railway  Motor  Load — Methods  of  Equating  Motor  Load — Heat- 
ing Value  of  the  Current — Determination  of  Effective  Current 
from  I2  Curve — Determination  by  Polar  Method — Average  Motor 
Potential — Rating  of  Railway  Motors — Motor  Capacity  and  Selec- 
tion— Motor  Speeds  and  Gearing — Use  of  Field  Control  Motors — 
Proper  Number  of  Motors — Power  Required  for  Alternating- 
Current  Motors — Energy  Required  for  Train  Operation — Kinetic 
Energy — Use  of  Straight  Line  Speed- Time  Curves — Energy  Con- 
sumption with  Electric  Motors — Effect  of  Gear  Ratio  on  Energy 
Consumption — Method  of  Comparing  Energy  Consumption — 
Watt-Hours  per  Ton-Mile— Influence  of  Train  Resistance  on 
Energy  Consumption — Effect  of  Length  of  Run  on  Energy — In- 


CONTENTS  ix 

PAGE 

fluence  of  Grades  on  Energy — Distribution  of  Energy  Input — 
Energy  for  Auxiliaries — Regeneration  of  Electric  Energy — Effects 
of  Regeneration  on  Equipment. 

CHAPTER  VII 

BRAKING  OF  ELECTRIC  RAILWAY  TRAINS 164 

Importance — Methods  Available  for  Retardation — Need  for 
Power  Brakes — Nature  of  Braking  Phenomena — Adhesion  Coef- 
ficient— Sliding  Friction — Effect  of  Distance  on  Sliding  Friction — 
Combined  Effect  of  Variations  in  Friction  Coefficient — Determina- 
tion of  Correct  Retardation — Transmission  of  Braking  Forces — 
Distribution  of  Forces  on  the  Car — Distribution  of  Forces  on  the 
Truck — Effect  of  Rotational  Inertia — Brake  Rigging — Truck 
Brake  Rigging — Foundation  Brake  Rigging — Automatic  Slack 
Adjuster — Methods  of  Supplying  Braking  Force — Hand  Brakes — 
Air  Brakes — Methods  of  Compressing  the  Air — Straight  Air 
Brakes — Automatic  Air  Brakes — Electropneumatic  Brake — Com- 
bined Straight  and  Automatic  Brake — Vacuum  Brake — Electric  and 
Magnetic  Brakes — Newell  Magnetic  Brake — Momentum  Brakes. 

CHAPTER  VIII 

CARS  AND  CAR  EQUIPMENT 200 

Classification — Structural  Classification  and  Development — Mate- 
rials of  Car  Construction — Framing — Roof  Farming — Door  Ar- 
rangement— Seating  Arrangement — Fare  Collection — Types  of 
Prepayment  Cars — Center  Entrance  Cars — Near-Side  Car — Rapid 
Transit  Cars — Interurban  Cars — Auxiliary  Electric  Devices — Car 
Lighting — Car  Heating — Electric  Heaters — Car  Wiring — Col- 
lectors— Car  Painting — Miscellaneous  Details  of  Car  Equipment — 
Trucks  and  Running  Gear — Single  Truck  Cars — Swiveling  Trucks — 
Maximum  Traction  Trucks — Motor  Suspensions — Motor  Gearing. 

CHAPTER  IX 

ELECTRIC  LOCOMOTIVES 240 

Development — Advantages  of  Motor-Car  Trains — Field  of  the 
Electric  Locomotive — Wheel  Classification — Electric  Locomotive 
Types — Application  of  Locomotive  Types — Geared  and  Gearless 
Motors — Number  and  Coupling  of  Drivers — Interchangeability  of 
Locomotives  —  Tractors —  Locomotive  Equipment  —  Locomotive 
Control — Choice  of  Locomotives. 

CHAPTER  X 

SELF-PROPELLED  CARS 254 

Field  of  Self-Propelled  Cars — Gasoline  Cars — Gas-Electric  Cars — 
Storage  Battery  Cars — Comparison  of  Self-Propelled  Cars — 
Gasoline  and  Special  Locomotives. 


x  CONTENTS 

CHAPTER  XI 

PAGE 

ELECTRIC  RAILWAY  TRACK 261 

Track  Construction — Track  Rails — Rail  Joints — Track  Construc- 
tion on  Paved  Streets — Special  Forms  of  Rail  Joints — Cast  Welded 
Joints— Thermit  Weld— Electric  Welding— Special  Work. 

CHAPTER  XII 

THE  DISTRIBUTING  CIRCUIT 270 

The  Electric  Railway  Circuit — Use  of  Graphical  Time-Table — • 
Limiting  Drop — Methods  of  Feeding — Use  of  Boosters — Require- 
ments of  the  Contact  Line — Forms  of  Contact  Line — The  Over- 
head Trolley — Methods  of  Suspending  Trolley  Wire — Catenary 
Suspension — Methods  of  Supporting  Wires — Use  of  Supporting 
Bridges — Size  of  Contact  Conductor — The  Third  Rail — Over- 
Running  Third  Rail — Under-Running  Third  Rail — Underground 
Conduit  Systems — Surface  Contact  Systems — The  Return  Circuit 
— Use  of  Rails  as  a  Conductor — Track  Bonding — Resistance  of  the 
Return  Circuit — Reactance  of  Rails — Defects  in  the  Return  Cir- 
cuit— Electrolysis — Remedies  for  Electrolysis — Polarity  of  the 
Direct-Current  Circuit — Alternating  Currents  and  Electrolysis — 
Special  Methods  of  Feeding. 

CHAPTER  XIII 

SUBSTATIONS  FOR  ELECTRIC  RAILWAYS 305 

Historical  Sketch  of  Development — Complex  Distribution  Systems 
— Types  of  Converters — Motor- Generator  Sets — Synchronous 
Converters — The  Motor-Converter — The  Permutator — The  Mer- 
cury Vapor  Rectifier — Mechanical  Rectifiers — Comparison  of 
Converters — Substation  Equipment — Storage  Batteries  in  Sub- 
stations— Classes  of  Distribution  Systems — Location  and  Capacity 
of  Substations — Location  of  City  Substations — Location  of  Sub- 
stations for  Interurban  Roads — Effect  of  Potential  on  Substation 
Spacing — Alternating-Current  Distribution — Portable  Substations. 

CHAPTER  XIV 

THE  TRANSMISSION  CIRCUIT 324 

Development — Types  of  Transmission  Circuits — Need  for  High 
Tension — Choice  of  Potential — Regulation  of  the  Transmission 
Line — Mechanical  Arrangements  of  Transmission  Lines. 

CHAPTER  XV 

POWER  GENERATION 330 

Requirements — Capacity  of  the  Power  Station — Power  Plant 
Location — Hydraulic  Power — Choice  of  Equipment — Power  Plant 
Construction — Purchased  Power. 


CONTENTS  xi 

CHAPTER  XVI 
/  PAGE 

SIGNALS  FOR  ELECTRIC  ROADS 335 

Uses  of  Signals — Kinds  of  Signals — Methods  of  Displaying  Indi- 
cations— Signal  Indications — Methods  of  Train  Spacing — Time 
Interval  Operation — Train  Order  Dispatching — The  Space  Inter- 
val— Telegraphic  Block — Controlled  Manual  System — Automatic 
Block  Signals — Wire  Circuit  Signals — Continuous  Track  Circuit 
Signals — Track  Circuits  for  Electric  Railways — Single  Rail  Sys- 
tem— Double  Rail  Alternating-Current  System — Methods  of  Op- 
erating Semaphores — Permissive  Operation — Preliminary  Signals 
— Signals  for  Operation  in  Two  Directions — Cab  Signals — The 
Automatic  Stop — Automatic  Train  Control — Interlocking. 

CHAPTER  XVII 

SYSTEMS  FOR  ELECTRIC  RAILWAY  OPERATION 355 

600-Volt  Direct-Current  System — High-Tension  Direct-Current 
Systems — Three-Phase  System — The  Single-Phase  Alternating- 
Current  System — Field  of  the  Systems. 

CHAPTER   XVIII 

ENGINEERING  PRELIMINARIES 365 

Electric  Railway  Location — City  Roads — Future  Requirements — 
Number  of  Cars — Size  and  Type  of  Cars — Schedule  and  Maximum 
Speeds — Interurban  Roads — Operating  Expenses — Estimation  of 
Construction  Cost — Net  Receipts — Steam  Road  Electrification- 
Choice  of  System. 

INDEX 377 


THE  ELECTRIC  RAILWAY 


CHAPTER  I 
INTRODUCTION 

The  Requirements  of  Transportation. — The  problem  of  trans- 
portation is  one  of  the  greatest  in  engineering;  in  many  respects 
it  is  the  most  potent  factor  in  our  modern  civilization.  When 
communities  were  small  and  self-contained,  there  was  little  need 
for  other  than  local  service.  As  soon  as  it  was  found  that  a 
community  could  produce  more  of  a  commodity  than  was  needed 
for  local  consumption,  while  at  the  same  time  it  lacked  in  other- 
necessities,  an  interchange  of  such  products  was  found  desirable 
and  even  necessary.  With  this  traffic  came  a  need  for  passenger- 
transportation,  since  agents  were  required  to  attend  to  the 
necessary  transactions  due  to  the  traffic  developed. 

Ever  since  the  beginning  of  history  this  interchange  of  merchan- 
dise has  been  one  of  the  great  vocations  of  mankind.  Until 
about  the  beginning  of  the  nineteenth  century  the  traffic  on 
land  was  handled  exclusively  by  animal  power.  As  the  result 
of  experiments  made  by  a  number  of  investigators  in  the  first 
portion  of  the  last  century,  mechanical  means  of  transportation 
were  made  available.  The  motive  power  thus  invented  was  the 
steam  engine,  which  was  developed  into  the  prototype  of  its 
modern  form  when  Stephenson's  " Rocket"  was  built  in  1829. 
The  results  attained  as  the  outcome  of  this  invention  were  far- 
reaching;  it  entirely  revolutionized  all  methods  of  transportation. 

The  problems  involved  in  railway  service  are  many  and  varied. 
Although  transportation  is  one  of  the  earliest  activities  of  man- 
kind, the  modern  railroad  really  had  its  beginning  with  the  use 
of  steam  as  a  motive  power,  in  the  early  part  of  the  nineteenth 
century.  From  humble  beginnings,  it  soon  developed  along  two 
radically  different  lines:  the  main-line  or  "trunk"  railroad,  and 
the  street  railway  or  "  tram  way." 

1 


2  '  :  'T&&  ELECTRIC  RAILWAY 

The  Trunk  Line  Railroad. — This  is  usually  considered  to  be  a 
line  of  considerable  length,  handling  traffic  in  large  units  and  at 
moderate  or  high  speeds.  In  most  cases  the  trunk  railway  has 
been  built  to  meet  the  demand  for  a  transfer  of  commodities 
from  point  of  production  to  point  of  consumption,  and  inciden- 
tally to  handle  the  passenger  traffic  originating  in  its  territory. 
Such  a  road  is  one  connecting  a  number  of  cities  of  large  size, 
and  handling  all  classes  of  freight  and  passenger  service.  On 
this  type  of  railway  the  freight  business  is  usually  of  greater 
importance  than  the  passenger,  the  latter  often  being  handled 
merely  as  a  necessary  incident  to  operation. 

The  Street  Railway. — The  street  railway  has  been  developed 
along  radically  different  lines,  and  is  a  direct  result  of  the  growth 
of  communities.  At  the  beginning  of  the  nineteenth  century, 
the  area  of  the  largest  of  cities  was  sufficiently  small  that  prac- 
tically all  residents  could  have  their  homes  within  reasonable 
walking  distance  of  their  work.  As  towns  grew  larger,  more 
rapid  means  of  transportation  became  imperative  to  prevent 
unnecessary  waste  of  time  in  going  to  and  from  business.  The 
earliest  solution  of  the  problem  was  the  use  of  the  omnibus, 
which  increased  slightly  the  radius  within  which  a  worker  could 
choose  his  home.  From  this  to  the  "  tram-car"  or  horse-car 
was  a  short  step,  the  difference  consisting  merely  in  adapting  the 
omnibus  to  run  on  a  track  laid  in  the  city  streets.  The  horse 
railway  was  developed  for  about  50  years,  reaching  its  zenith 
in  the  early  eighties.  The  possible  increase  of  schedule  speed, 
depending  as  it  did  on  the  physical  capacity  of  the  horse,  reached 
its  maximum  soon  after  the  introduction  of  this  type  of  motive 
power.  This  limitation  became  so  serious  that  mechanical 
devices  were  sought  to  increase  the  possibilities  of  the  street 
railway.  Steam,  gasoline,  compressed  air  and  the  cable  were  all 
tried,  with  varying  degrees  of  success. 

The  Cable  Railway. — Of  these  motive  powers,  the  cable  was 
the  only  one  that  gave  anything  like  satisfactory  service.  Intro- 
duced in  1873,  a  number  of  cable  lines  were  installed  in  the 
succeeding  20  years,  and  operated  with  varying  degrees  of  success. 
The  salient  feature  of  this  system  was  a  wire  rope,  driven  by  a 
steam  engine,  and  running  the  entire  length  of  the  track  in  a 
slotted  conduit  of  concrete  and  iron,  located  between  the  run- 
ning rails.  Power  was  transmitted  to  the  car  by  mechanical 
clutches  or  " grips"  fastened  to  the  car  body,  and  extending 


INTRODUCTION  3 

into  the  conduit  to  engage  the  cable.  Starting  the  car  consisted 
in  clutching  the  cable  with  the  grip,  and  in  that  way  obtaining 
the  necessary  force  to  move  the  train.  It  is  evident  that  only 
one  speed  was  possible;  and,  due  to  the  constructional  features 
of  the  system,  the  velocity  was  limited  to  about  10  miles  per  hr. 
The  starting  conditions  were  also  bad.  Either  the  train  would 
start  with  a  jerk,  or  else  the  grip  would  slide  along  the  cable 
before  catching  hold  of  it,  causing  excessive  wear.  Cables  of 
the  size  used  were  expensive,  and  were  subject  to  frequent 
breaks,  necessitating  complete  shut-downs  of  the  system  during 
repairs.  On  account  of  the  design,  the  cost  of  construction  was 
almost  prohibitive,  being  over  $100,000  per  mile  of  track.  Only 
the  most  densely  populated  cities  could  furnish  sufficient  traffic 
to  warrant  the  installation  of  the  system. 

The  Electric  Street  Railway.— In  1884  the  first  practical 
electric  railway  in  the  United  States  was  put  in  operation  at 
Cleveland,  Ohio,  by  Edward  M.  Bentley  and  Walter  H.  Knight. 
Almost  immediately  afterward  a  number  of  other  electric  roads 
commenced  running;  and  it  became  apparent  at  once  that  the 
use  of  electricity  furnished  a  satisfactory  solution  of  the  problem 
of  giving  rapid  transit  to  cities.  Its  application  spread  quickly, 
until  today  it  is  the  only  power  considered  for  this  class  of 
service.  It  has  also  replaced  all  the  other  methods  of  opera- 
tion which  have  been  tried  from  time  to  time;  and  has  per- 
mitted of  extensions  and  forms  of  service  out  of  the  question  with 
other  motive  powers. 

The  Interurban  Railway. — In  connection  with  many  city 
railway  systems,  it  was  found  possible  to  develop  a  profitable 
suburban  passenger  business,  usually  serving  city  workers  who 
desired  to  live  in  the  country,  and  were  willing  to  spend  a  little 
more  time  in  traveling  than  the  ordinary  city  resident.  In 
many  cases  this  brought  the  electric  roads  into  active  com- 
petition with  parallel  steam  roads.  Almost  without  exception 
the  former  were  able  to  handle  this  class  of  traffic  better  than 
their  competitors,  so  that  today  the  steam  roads  have  been  prac- 
tically driven  out  of  the  suburban  business. 

The  success  of  suburban  roads  encouraged  promoters  to 
venture  further  into  the  steam  railway  field  by  building  lines 
between  centers  of  business  for  the  handling  of  passenger  traffic. 
These  interurban  railways  have  usually  been  successful,  since 
their  relations  with  the  city  lines  have  enabled  them  to  give 


4  THE  ELECTRIC  RAILWAY 

better  service  than  the  steam  roads,  even  though  their  schedule 
speeds  are  ordinarily  lower.  These  roads  have  developed  an 
entirely  new  class  of  business — a  passenger  traffic  between  the 
rural  districts  and  the  cities.  Farmers  have  found  it  easier  to 
use  the  electric  passenger  cars  than  to  drive  their  teams  to 
the  towns.  As  a  consequence  they  travel  much  more  than 
they  formerly  did.  This  rural  traffic  has  in  turn  caused  a  demand 
for  an  express  and  package  freight  service  on  the  interurban 
lines.  Such  business  is  usually  quite  profitable  to-  the  rail- 
ways, being  handled  by  the  regular  passenger  trains  with  little 
extra  cost.  In  some  few  cases,  the  growth  of  this  business 
has  been  so  great  that  it  has  been  found  impossible  to  accommo- 
date it  with  the  passenger  equipment;  and  regular  freight  and 
express  trains  are  operated  entirely  apart  from  the  passenger 
business. 

Scope  of  the  Electric  Railway. — During  its  30  years  of  suc- 
cessful development,  the  scope  of  the  electric  railway  has  broad- 
ened materially.  Not  content  with  city  operation  alone,  the 
managers  of  city  roads  have,  as  just  stated,  extended  them  to 
embrace  suburban  and  interurban  passenger  service.  These 
latter  developments  were  not  made  without  opposition  from  the 
established  steam  lines  with  which  they  competed;  but  within 
the  past  few  years  the  steam  railways  have  realized  the  possi- 
bilities of  utilizing  electric  power  on  their  own  systems  for  serv- 
ing the  same  class  of  traffic. 

At  the  present  time  the  use^of  electricity  for  the  hauling  of 
freight  is  quite  limited,  and  by  far  the  larger  number  of  electric 
roads  are  equipped  for  the  handling  of  passenger  trains  ex- 
clusively. Electric  freight  service  is,  however,  expanding 
rapidly,  and  it  will  not  be  surprising  to  find  many  railroads  us- 
ing electric  power  for  this  purpose  within  the  next  decade."") 

Many  steam  roads  have  seriously  considered  the  use  of 
electricity  on  certain  divisions,  and  several  have  already  made 
the  change.  The  operation  of  such  lines  as  have  been  electrically 
equipped  has  been  so  highly  satisfactory  as  to  warrant  the 
further  extension  of  the  system  in  practically  all  cases.  By  this 
it  must  not  be  understood  that  electric  power  is  a  universal 
panacea,  as  has  been  assumed  by  some  persons;  but  that,  when 
correctly  applied  and  intelligently  used,  it  may  effect  certain 
operating  economies  which  will  make  it  desirable. 


INTRODUCTION  5 

Classification  of  Railways. — For  purposes  of  study,  railways 
may  be  divided  roughly  into  three  main  groups: 

1.  Street  railways  ("tramways"). 

2.  Suburban  and  interurban  railways. 

3.  Trunk-line  railways. 

The  first  group  consists  of  roads  with  light  rolling  stock,  the 
operation  of  which  involves  many  stops  and  low  schedule  speeds. 
Since  the  distance  covered  by  a  car  in  a  given  time  is  propor- 
tional to  the  schedule  speed,  it  is  necessary  to  bring  it  from 
rest  to  a  fairly  high  velocity  in  a  short  time,  and  to  stop  it 
quickly.  Such  a  run  demands  high  rates  of  acceleration.  This 
class  of  road  is  exclusively  for  passenger  service. 

The  second  group  comprises  roads  using  considerably  heavier 
rolling  stock  than  the  first,  with  fewer  stops  and  at  higher  speeds. 
On  account  of  the  smaller  number  of  stops  the  demands  on  the 
motive  power  are  not  so  severe  as  in  the  first  class.  Many 
roads  in  this  group  handle  express  and  light  freight,  some  of 
them  obtaining  a  considerable  share  of  the  total  revenue  from 
these  sources. 

The  third  group  is  made  up  of  the  heaviest  classes  of  service, 
involving  both  passenger  and  freight  business.  The  passenger 
runs  are  in  general  of  considerable  length  and  at  high  speeds. 
On  such  roads  the  suburban  and  local  passenger  business,  al- 
though appearing  a  large  item  to  the  casual  observer,  is  a  com- 
paratively small  portion  of  the  total.  The  net  earnings  depend 
almost  entirely  on  the  handling  of  heavy  freight. 

The  above  classification  of  railways  is  by  no  means  absolute. 
A  considerable  number  of  suburban  roads  will  fall  between  the 
first  and  the  second  groups,  the  cars  being  either  the  same  as 
those  for  city  lines,  or  slightly  heavier,  and  operating  from 
the  center  of  a  city  into  its  suburbs.  Similarly,  a  number  of 
interurban  roads  approach  very  nearly  to  the  third  group,  al- 
though their  rolling  stock  and  schedules  do  not  justify  classifica- 
tion with  it.  Elevated  and  subway  service  is  in  general  a 
compromise  between  the  first  and  the  second  groups,  although 
not  belonging  to  either;  for  it  combines  the  requirements  of  a 
considerable  number  of  stops  and  a  high  schedule  speed.  The 
rolling  stock  is  moreover  of  such  a  weight  as  to  justify  its  classi- 
fication in  the  second  group. 


THE  ELECTRIC  RAILWAY 


Motive  Powers.  The  Steam  Locomotive. — For  railway  serv- 
ice, a  number  of  different  motive  powers  have  been  suggested, 
and  some  of  them  actually  used.  A  brief  description  of  them 
will  aid  in  understanding  the  conditions  in  the  motive  power 
field,  and  the  place  the  electric  system  has  in  it. 

The  steam  locomotive  has  excellent  characteristics  for  heavy 
railway  service.  It  is  unique  among  motive  powers  in  that  it 
comprises  in  itself  a  complete  steam  power  plant.  The  capacity 
of  a  locomotive  depends  on  two  main  factors:  the  size  of  the 
boiler  and  the  size  of  the  cylinders.  At  slow  speeds,  the  tractive 
effort  is  produced  by  the  maximum  pressure  of  the  steam  against 
the  piston.  This  maximum  pressure  may  be  maintained 
practically  constant  so  long  as  the  boiler  is  able  to  supply  steam 


yjVW 

40000 

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£   .  30000 

J 
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Freight 

\ 

Passeno 

\ 

v 

\ 

\ 

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^ 

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£      10000 
0 

^< 

^ 

<*.. 

---  — 

—  — 

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i 

>            10            15           TO           25            30          35           40 
Speed,    M.  P.  H. 

FIG.  1. — Characteristics  of  typical  steam  locomotives. 

to  the  cylinders.  Since  the  number  of  strokes,  and  hence  the 
quantity  of  steam  used,  varies  directly  with  the  speed,  a  point 
must  be  reached  where  the  boiler  cannot  keep  up  its  pressure 
against  the  increasing  demand  for  steam.  To  reach  higher  speeds 
the  cut-off  must  be  advanced,  so  that  the  amount  of  steam  taken 
per  stroke  is  reduced.  The  higher  the  speed,  the  earlier  must 
be  the  cut-off,  and  hence  the  less  the  mean  effective  pressure  and 
the  tractive  effort.  This  is  shown  graphically  in  Fig.  1,  which 
gives  a  tractive  effort-speed  curve  of  a  modern  passenger  engine 
and  of  a  modern  freight  engine.  In  the  high-speed  portion  of 
the  curve  the  locomotive  is  virtually  a  constant  power  machine, 
since  the  tractive  effort  varies  almost  inversely  as  the  speed. 


INTRODUCTION  7 

The  performance  of  the  cylinders  is  hampered,  since  they  rely 
for  their  steam  on  a  boiler  of  limited  capacity.  The  boiler  in 
turn  is  dependent  on  the  fire-box  and  the  ability  of  the  fireman 
to  keep  it  properly  supplied  with  fuel.  Owing  to  the  necessity 
of  getting  maximum  capacity  per  unit  of  weight,  the  performance 
is  forced  beyond  the  most  efficient  operating  point.  The  draft 
is  so  great  that  a  large  portion  of  the  fuel  (in  case  coal  is  used)  is 
thrown  out  of  the  stack  in  the  form 'of  cinders.  Tests  show  that 
approximately  one-tenth  of  the  total  weight  of  coal  fired  is  dis- 
charged in  this  manner.  Although  it  may  be  possible,  by  the 
use  of  special  precautions,  to  operate  the  steam  locomotive  with- 
out smoke  or  dirt,  it  is  in  general  impractical  to  do  so.  Since 
the  entire  power  plant,  and  also  a  supply  of  fuel  and  water, 
must  be  hauled  in  addition  to  the  train,  there  is  a  distinct  loss 
of  efficiency  due  to  that  cause. 

The  steam  locomotive  is  most  efficient  when  built  in  the 
larger  sizes,  since  many  of  the  losses  are  nearly  constant,  or 
increase  more  slowly  than  in  proportion  to  the  weight.  The 
limit  is  reached  only  by  the  ability  of  the  fireman  to  handle  the 
necessary  amount  of  coal.  In  some  recent  locomotives  mechan- 
ical stokers  are  used,  resulting  in  some  increase  in  capacity  over 
hand  firing.  In  the  smallest  sizes,  the  steam  locomotive  is 
decidedly  inefficient,  and  in  many  respects  is  not  the  excellent 
machine  that  has  been  developed  by  the  designers  of  modern 
large  engines. 

Other  Motive  Powers. — Gasoline  and  other  fuel  oils  have 
been  used  in  connection  with  internal  combustion  engines. 
While  these  combinations  are,  in  common  with  the  steam 
locomotive,  complete  power  plants,  they  are  considerably  simpler, 
and  are  lighter  than  it  per  unit  of  output.  They  also  operate 
with  but  a  small  fraction  of  the  smoke  and  dirt  incident  to  the 
steam  locomotive.  The  internal  combustion  motor  is  in- 
herently a  constant-speed  machine,  and  special  means  must  be 
employed  to  reduce  speeds  at  starting  and  for  slow  running.  In 
the  automobile  this  is  brought  about  by  changes  of  gearing,  and 
variations  in  the  amount  of  charge  and  the  time  of  its  ignition. 
At  best  these  methods  give  an  imperfect  speed  control;  and  they 
are  not  very  practical  for  heavy  train  service. 

Compressed  air  and  stored  steam  have  also  been  tried  for 
motive  powers.  The  engines  are  similar  to  the  ordinary  loco- 
motive steam  engine,  but  are  supplied  from  tanks  on  the  loco- 


8  THE  ELECTRIC  RAILWAY 

motive  containing  either  steam  or  air  compressed  to  a  high 
pressure.  Owing  to  the  high  storage  capacity  necessary,  and  to 
the  low  thermodynamic  efficiency  of  the  complete  cycle,  they 
have  not  been  successful.  A  few  locomotives  of  these  types 
are  used  in  mines,  where  the  fire  of  the  steam  locomotive  would 
be  liable  to  cause  explosions  of  the  mine  gases. 

The  cable  has  already  been  mentioned.  It  was  never  suited 
to  any  class  of  service  except  in  congested  city  districts,-  and  even 
there  its  limitations  forced  its  retirement  as  soon  as  a  better 
motive  power  was  available.  At  the  present  time  the  only  roads 
operated  by  cable  are  in  a  few  places  where  the  grades  are  so 
steep  that  some  form  of  positive  drive  is  necessary. 

Electric  Systems. — For  railway  service,  there  is  available  a 
number  of  combinations  of  motors  and  electric  circuits,  giving  an 
almost  unlimited  flexibility,  and  enabling  the  engineer  to  choose 
the  best  type  of  equipment  for  each  case.  In  fact,  this  wide 
range  of  choice  is  one  of  the  factors  which  has  prevented  earlier 
consideration  of  electrification  by  steam  railroad  managers,  who 
are  to  a  certain  extent  awaiting  the  standardization  of  one  or 
another  of  the  principal  systems  of  electric  operation. 

Although  practically  every  type  of  electric  motor  ever  built 
has  been  used  or  suggested  for  traction  at  one  time  or  another, 
there  are  in  use  three  systems  which  have  driven  out  all  others 
for  practical  service: 

1 .  The  direct-current  system,  using  series-wound  motors. 

2.  The  single-phase  alternating-current  system,  using 
(a)  Single-phase  commutator  motors,  or 

(6)  Three-phase  induction  motors  operated  through 
a  "  split-phase  converter." 

3.  The   three-phase   alternating-current   system,  using 
three-phase  induction  motors. 

It  is  beyond  the  scope  of  the  present  chapter  to  present  an 
extended  discussion  and  comparison  of  the  different  electric 
systems.  They  will  be  taken  up  part  by  part  in  later  chapters, 
with  a  summary  under  "  Systems  of  Electrification."  In  general, 
the  direct-current  series  motor  and  some  of  the  alternating- 
current  commutator  motors  possess  characteristics  quite 
similar  to  those  of  the  steam  locomotive  engine,  with  even  better 
performance  at  starting;  while  the  induction  motors  operate  at 
substantially  constant  speed  throughout  their  working  range. 
The  speed  of  each  type  may  be  reduced  for  starting  or  slow  run- 


INTRODUCTION  9 

ning  by  purely  electrical  means,  thus  obviating  the  necessity  of 
change  gears,  as  with  the  internal  combustion  engines.  The 
efficiency  of  each  is  high,  and,  including  all  losses  in  genera- 
tion and  distribution,  is  at  least  as  good  as  that  of  the  steam 
locomotive. 

Of  the  three  systems,  the  direct-current  has  been  in  use  the 
longest  time.  All  of  the  early  experiments  were  made  with 
direct-current  motors ;  and  for  about  20  years  alternating  current 
was  not  even  thought  of  in  connection  with  railway  operation. 
It  is  evident  that  the  direct-current  motor,  having  passed  through 
a  long  stage  of  experimentation  and  development,  has  reached 
the  highest  state  of  perfection  at  the  present  time.  All  railways 
of  the  first  class  (street  railways)  are  operated  by  this  system; 
and  in  this  kind  of  service  it  has  proved  eminently  satisfactory. 
Whether  it  will  maintain  its  excellent  reputation  in  the  heavier 
classes  of  traction  remains  to  be  proved. 

Advantages  of  Electric  Systems. — As  compared  with  other 
motive  powers,  electric  motors  possess  a  number  of  marked 
advantages.  They  may  be  enumerated  as  follows: 

(a)  The  heavy  overloads  that  may  be  imposed  on  the 
electric  motor  for  a  short  time. 

(b)  The  great  starting  ability  due  to  the  economical  distri- 
bution of  weight. 

(c)  The  absence  of  reciprocating  parts,  giving  a  uniform 
torque. 

(d)  The  cleanliness  and  noiselessness   of  this  method   of 
operation. 

(e)  The  ease  and  economy  of  control  of  the  motors. 

(/)  The  high  efficiency  of  the  electric  motor  and  distribu- 
tion systems  as  applied  to  traction. 

Electric  motors  of  the  types  used  for  traction  are  capable  of 
withstanding  heavy  overloads.  In  fact,  if  properly  designed  for 
its  continuous  capacity,  a  motor  may  be  loaded  until  stopped 
without  harm  to  it,  unless  the  overload  be  too  prolonged.  This 
characteristic  is  of  great  value  when  there  is  difficulty  in  starting 
a  train  due  to  any  cause. 

The  weight-distribution  of  electric  motive  powers  is  excellent. 
In  the  case  of  motor  cars,  all  of  the  train  weight  may  be  made 
available  for  adhesion,  by  placing  a  motor  on  each  axle.  This 
maximum  adhesion  is  seldom  demanded;  although  for  a  number 
of  reasons  single  cars  are  often  equipped  with  four  motors.  In 


10  THE  ELECTRIC  RAILWAY 

steam  locomotives,  a  considerable  proportion  of  the  total  weight 
is  in  the  tender  with  its  load  of  fuel  and  water.  Not  only  is  this 
feature  absent  in  the  electric  locomotive,  but  a  larger  portion  of 
the  weight  of  the  locomotive  proper  may  be  placed  on  the  drivers. 
The  effect  of  this  is  that  the  electric  engines  will  be  much  the 
lighter  for  the  same  hauling  power. 

In  the  steam  locomotive,  the  tractive  effort  in  one  revolution 
of  the  drivers  varies  over  a  considerable  range,  due  to  the  non- 
uniform  effort  of  the  steam  during  the  stroke  of  the  piston.  In 
some  cases  this  will  cause  slipping  of  the  wheels  before  the  average 
value  of  the  maximum  tractive  effort  is  reached.  In  the  electric 
locomotive  the  torque  may  be  applied  up  to  the  slipping  point 
of  the  wheels  without  difficulty,  since,  due  to  the  symmetrical 
design  of  the  motor  armature,  it  gives  the  same  torque  in  any 
position;  which  is  also  true  in  those  machines  where  the  force  is 
transmitted  through  cranks  and  side-rods,  if  the  cranks  be 
"  quartered,"  as  is  the  usual  practice. 

The  cleanliness  of  electric  motors,  as  compared  with  steam 
engines,  is  unquestioned.  In  fact,  this  feature  is  one  of  those 
that  have  made  rapid  transit  on  city  streets  satisfactory,  and  is 
the  one  thing  that  has  made  subway  and  tunnel  operation 
possible.  The  absence  of  smoke,  dust  and  cinders  is  a  great 
argument,  especially  since  a  measurable  financial  loss  is  in- 
volved in  the  dirt  incident  to  steam  operation.  The  view  has  been 
taken  by  the  courts  that  persons  living  along  the  line  of  a  steam 
road  in  a  city  can  recover  for  damage  due  to  these  causes.  Noise 
may  be  reduced  to  an  almost  negligible  amount  by  the  use  of 
properly  maintained  electrical  equipment,  something  impossible 
with  steam;  for  the  sharp  blast  of  the  exhaust  through  the 
nozzle  is  necessary  to  provide  sufficient  draft  in  the  fire-box. 

Electric  motors  of  the  various  types  may  be  controlled  by 
electrical  means  to  operate  at  various  speeds;  and  the  speed  may 
be  reduced  to  zero  for  starting  or  coupling  purposes.  Although 
there  are  some  losses  incident  to  greatly  reduced  speeds  which 
do  not  appear  with  steam  locomotives,  they  do  not  compare 
unfavorably  with  losses  in  the  control  of  other  motive  powers. 

Traction  motors  are  usually  designed,  not  for  high  efficiency, 
but  for  ruggedness  and  reliability.  Commercial  machines  have 
very  good  efficiencies,  however.  The  overall  efficiency  of  the 
complete  electric  system  will  vary  from  50  per  cent,  to  75  per 
cent,  in  ordinary  cases.  Although  at  first  sight  these  values  may 


INTRODUCTION  11 

appear  low,  they  are  in  reality  excellent,  and  better  than  those  of 
other  motive  power  systems  employed  in  similar  service. 

The  advantages  enumerated  above  are  most  marked  in  the 
first  and  second  classes  of  roads;  but  nearly  all  of  them  are 
applicable  to  the  third  class  also.  They  are  likewise  greater  in 
the  case  of  motor  car  operation  than  when  the  power  is  con- 
centrated in  locomotives,  though  the  use  of  the  latter  introduces 
certain  compensating  advantages  which  often  more  than  offset 
the  detriments. 

In  general,  the  superiority  of  electric  power  is  great  enough  to 
warrant  its  consideration  for  any  class  of  railway  service;  and 
its  use  is  the  more  desirable  almost  in  proportion  to  the  density  of 
the  traffic,  either  freight  or  passenger. 

The  Railway  Problem. — In  a  broad  sense,  the  railway  has 
much  in  common  with  other  engineering  works.  Speaking 
generally,  what  is  desired  is  to  perform  certain  functions  for  the 
benefit  of  the  public,  at  the  same  time  making  a  reasonable 
profit  on  the  invested  capital.  In  attacking  any  problem  of 
this  character,  it  is  necessary  to  consider  all  phases  of  it  in 
determining  whether  a  project  is  attractive  for  the  investor. 
To  do  this,  certain  engineering  points  must  be  considered  in 
detail,  and  assumptions  made  and  proved  correct.  In  the 
following  chapters  the  engineering  methods  are  discussed  sepa- 
rately; but  the  main  object,  as  given  in  this  paragraph,  must  not 
be  lost  sight  of. 


CHAPTER  II 
THE  MECHANICS  OF  TRACTION 

Fundamental  Principles. — The  fundamental  relations  govern- 
ing the  motion  of  railway  trains  are  derived  directly  from  the 
laws  of  motion  of  any  material  bodies.  For  convenience  in 
calculation  a  number  of  secondary  units  have  been  derived  for 
the  solution  of  railway  problems.  Since  these  units  are  almost 
universally  employed  in  the  literature  of  the  subject,  a  brief 
review  of  their  derivation  is  desirable. 

Work  and  Energy. — When  a  material  body  is  moved  over  a 
given  distance,  mechanical  energy  is  expended  and  work  is 
done.  By  the  principle  of  the  conservation  of  energy,  the  two 
must  be  equal,  and  the  numerical  measure  of  either  is  the  product 
of  the  force  employed  into  the  distance  over  which  the  body 
has  moved,  or 

W  =  Fs  (1) 

where  W  is  the  energy  or  work,  F  is  the  force  employed,  and 
s  is  the  distance  over  which  the  body  is  moved. 

The  above  equation  expresses  the  potential  energy  of  the  body. 
If  we  consider  a  body  in  motion,  especially  if  the  force  be  a  vari- 
able one,  the  equation  must  be  made  to  express  momentary 
changes  of  distance  covered,  or 

dW  =  Fds  (2) 

From  equation  (2)  may  be  derived  the  total   energy  or  work 
done,  by  the  integration, 

W  =   fFds  (3) 


In  order  to  apply  equation  (3),  it  is  necessary  to  estimate 
the  change  in  the  distance  covered  at  each  portion  of  the  motion. 
This  is  most  readily  done  by  means  of  the  velocity,  which  is  the 
rate  of  change  of  position  with  respect  to  time,  or 

ds 


12 


THE  MECHANICS  OF  TRACTION  13 

This  may  also  be  written 

ds  =  vdt  (4a) 

where  v  is  the  velocity,  and  t  the  time. 

If  we  use  this  last  value  in  the  above  equation  for    energy, 
(2),  it  becomes 

dW  =  Fvdt  (5) 

From  elementary  mechanics  we  have 

W  =  %-Mv*  (6) 

where  M  is  the  mass  of  the  body  in  motion. 

A  differentiation  of  this  last  equation,   (6),  with  respect  to 
Vj  gives 

dW  =  Mvdv  (7) 

Acceleration. — We  may  now  equate  the  two  expressions  for 
differential  energy,  (5)  and  (7),  or 

Fvdt  =  Mvdv  (8) 

whence 

F  =  M  -j-  (8a) 

In  this  equation,  -77,  the  rate  of  change  of  velocity  with  respect 
to  time,  is  better  known  as  the  acceleration,  a,  or 

F  =  Ma  (9) 

Equation  (9)  holds  good  in  any  system  of  notation.  In  countries 
where  the  English  system  of  units  is  employed,  the  force  F  and 
the  mass  M  are  usually  measured  in  pounds,  and  acceleration  a 
in  feet  per  second  per  second.  Since  masses  are  usually  estimated 
by  gravity-measure,  it  is  customary  to  restate  equation  (9)  as 

'-?•  (10) 

where  G  is  the  weight  of  the  moving  body  and  g  the  acceleration 
due  to  gravity.  In  the  English  system  the  "  gravitation  con- 
stant" g  has  a  value  of  approximately  32.2,  whence 

F  =  3^2  a  (10tt) 

and 

a  =  — '„ — 


14  THE  ELECTRIC  RAILWAY 

In  equations  (10a)  and  (106)  acceleration  a  is  expressed  in  feet  per 
second  per  second,  and  force,  F,  and  weight,  G,  in  pounds.  For 
use  in  railway  problems  these  units  are  inconvenient,  the  speeds 
being  more  readily  determined  in  miles  per  hour  and  the  accelera- 
tions in  miles  per  hour  per  second  ;  and  the  weights  are  of  such 
magnitude  that  they  are  better  expressed  in  tons  (in  the  United 
States  the  short  ton  of  2000  Ib.  is  now  universally  used). 
Formula  (10a)  and  (106)  must  therefore  be  modified  for  prac- 
tical use.  A  mile  contains  5280  feet,  and  an  hour  60  X  60  = 

3600  seconds;  hence  a  velocity  of  l.mile  per  hr.  is  equal  to  O 


1.467  ft.  per  sec.     If  we  express  accelerations  in  miles  per  hour 
per  second  by  A,  then 

a    =  1.467A  (11) 

or 

'  A    =  0.682a  (llo) 

Employing  T  to  represent  weight  in  short  tons,  and  A  to 
denote  accelerations  in  miles  per  hr.  per  sec.,  as  given  in 
equations  (11)  and  (Ha),  equation  (10a)  becomes 


1.467  A 


2000  T 
whence 

A  =  0.01098  ~  (12) 

or,  solving  for  F, 

F  =  91.097  TA  (13) 

or,  in  other  words,  a  force  of  91.1  Ib.  applied  to  a  body  weighing 
1  ton  will  produce  in  it  an  acceleration  of  1  mile  per  hr.  per 
sec.  Equations  (12)  and  (13)  are  the  ones  usually  employed 
in  discussing  acceleration  of  railway  trains. 

Rotational  Acceleration. — Besides  the  rectilinear  acceleration 
as  determined  above,  it  is  also  necessary  to  impart  to  the  wheels, 
axles,  gears  and  motor  armatures  a  motion  of  rotation.  To 
produce  this  rotational  acceleration  an  additional  amount  of 
force  must  be  employed.  This  may  be  determined  as  follows: 
Referring  to  Fig.  2,  consider  a  particle  of  mass  dM,  of  any  of  the 
rotating  parts  of  a  car,  situated  at  a  distance  p  from  the  center  of 
rotation.  If  the  angular  acceleration  of  the  rotating  part  be  0, 
the  tangential  acceleration  of  the  mass  dM  at  any  instant  will  be 


\ 
THE  MECHANICS  OF  TRACTION  15 

p0,  and,  from  equation  (9),  the  force /i  to  produce  that  accelera- 
tion is  pddM.  Since  the  force  /i  acts  at  a  distance  p  from  the 
center  of  rotation,  its  moment  is 

pBdM  X  p  =  p2BdM 
The  total  moment  of  the  whole  rotating  mass  is 

fp*edM  =  KB  (14) 

where  K  is  the  moment  of  inertia  of  the  body  about  its  axis  of 
rotation.  It  may  also  be  expressed  by  the  relation 


K  =  k2M  (15) 

where  k  is  the  radius  of  gyration  and 
M  the  total  rotating  mass.     Also 

re  =  a  (16) 

or 

a 


Accel.6 


r 


(16a) 


where  r  is  the  radius  of  the  rotating 
part  considered,  and  a  its  tangential 

acceleration.  FlG-    2.—  Determination    of 

rotational  acceleration. 
Hence 


Total  moment  =  k2M  (17) 

k2 
=  -Ma  (17o) 


and 

Moment 


Ma  (18) 

For  a  pair  of  ordinary  cast  iron  car  wheels  and  axle  the  weight 
is  approximately  1950  lb.,  and  the  ratio-  =0.64.  Substituting 
in  equation  (18), 

1Q50 

/i  =  (0.64) 2  X  32-2  a  =  24'80a 

This  gives  the  force  /i  Ib.  to  produce  a  corresponding  acceleration 
in  feet  per  second  per  second.     To  transform  the  equation  to  our 


16  THE  ELECTRIC  RAILWAY 

railway  system  of  units,  it  is  only  necessary  to  multiply  by  the 
constant  1.467.  Since  there  are  four  axles  and  pairs  of  wheels  on 
an  ordinary  car,  the  value  thus  found  should  be  multiplied  by  4, 
making  the  complete  expression  for  the  force  to  produce  angular 
acceleration  for  a  car  without  electrical  equipment 

/  =  24.80  X  1.467  X  4^  =  145.52  A 

When  motor  cars  are  considered,  an  additional,  amount  of 
force  must  be  employed  besides  that  for  angular  acceleration  of 
wheels  and  axles.  It  may  be  determined  in  the  same  manner  as 
outlined  above.1  The  values  will  vary  with  the  type  and  number 
of  motors  per  car  or  per  locomotive.  The  following  figures  are 
representative  of  American  practice:2 

PER  CENT.  OF  TOTAL  ACCELERATING  FORCE  REQUIRED  FOR  ROTATING 

PARTS 

Per  cent. 

Steam  locomotive  and  train 2-5 

Electric  locomotive  and  heavy  freight  train 5 

Electric  locomotive  and  high-speed  passenger  train. .  7 

High-speed  electric  motor  cars 7 

Low-speed  electric  motor  cars 10 

Total  Accelerating  Force. — The  total  force  required  to  pro- 
duce acceleration  both  of  translation  and  rotation  is 

F  =  91.1  TA  +  145.52A 
or 

F  =  91.1  A(!T  +  145.52)  (19) 

for  a  car  without  electrical  equipment. 

In  the  particular  case  of  a  27.5  ton  car  equipped  with  four 
38  kw.  motors,  and  geared  for  a  speed  of  50  miles  per  hr.,  the 
force  required  for  producing  rotational  acceleration  is  9.55  per 
cent,  of  that  necessary  for  rectilinear,  making  the  total  force  for 
an  acceleration  of  1  mile  per  hr.  per  sec.  equal  to  91.1  XI. 0955, 
or  99.8  Ib.  per  ton. 

In  general,  a  value  of  100  Ib.  per  ton  may  be  used  with  a 
fair  degree  of  accuracy  as  the  total  force  required  for  unit  ac- 
celeration for  electric  motor  cars,  so  that  equation  (19)  may  be 
rewritten : 

F  =100 A  (19a) 

iSee  also  Chapter  VIII,  "Effect  of  Rotational  Inertia." 
2  Standard    Handbook  for  Electrical  Engineers,  Sec.   13,  par.    88,  Third 
Edition. 


THE  MECHANICS  OF  TRACTION  17 

which  is  widely  used  in  practice  where  extreme  accuracy  is  not 
required.  In  this  book  it  will  be  used  as  a  correct  approximation. 
Train  Resistance. — When  a  train  is  in  motion,  a  number  of 
forces  are  always  at  work  tending  to  reduce  its  velocity.  Some 
of  them  are  always  present;  others  occur  only  under  certain 
conditions.  It  is  therefore  necessary  to  state  just  what  is  meant 
by  the  term  "  train  resistance."  As  ordinarily  defined,  it  is 
understood  to  include  those  forces  which  oppose  the  motion  of  a 
train  when  running  on  a  straight  level  track  at  constant  speed, 
and  in  still  air.  This  portion  of  the  train  resistance,  which 
is  inherent  to  operation  under  the  stated  conditions,  may  be 
divided  into  the  following  components: 

1.  Journal  friction. 

2.  Rolling  resistance. 

3.  Flange  friction. 

4.  Oscillatory  resistances. 

5.  Air  resistance. 

6.  Friction  of  motor  gears  and  bearings  (in  motor  cars 
only). 

The  above  resistances  are  always  acting  to  retard  the  motion 
of  a  train  when  operating  under  the  conditions  stated.  In  addi- 
tion to  these  components,  there  are  others  not  inherent  to  the 
motion  of  the  train  itself,  but  which  depend  on  special  condi- 
tions of  operation.  They  are: 

7.  Grade    resistance. 

8.  Curve  resistance. 

9.  Wind  resistance. 

These  additional  components  may  frequently  exceed  the  in- 
herent resistance  in  amount;  and  in  the  operation  of  freight 
trains  at  slow  speeds  they  are  usually  the  more  important.  They 
may  be  grouped  under  the  head  "incidental  resistances." 

Journal  Friction. — Friction  in  the  journals  of  ordinary  rolling 
stock  follows  the  laws  of  bearing  friction  in  general.  A  common 
form  of  car  bearing  is  shown  in  Fig.  3,  which  is  a  section  through 
the  standard  5  X  9  in.  journal  adopted  by  the  American  Electric 
Railway  Engineering  Association.  The  axle  is  extended  to  form 
the  journal,  /,  which  rotates  in  the  journal  bearing  or  "brass," 
B.  Lubrication  is  provided  by  placing  a  quantity  of  oil-soaked 
wool  waste  in  the  oil  cellar,  C.  This  packing  carries  oil  from 
the  cellar  to  the  journal  by  capillary  attraction,  and  so  serves  to 


18 


THE  ELECTRIC  RAILWAY 


lubricate  the  bearing.  The  principle  of  lubrication  in  such  a 
bearing  depends  on  sufficient  oil  being  drawn  between  the 
journal  and  the  brass  to  form  a  film  of  lubricant  separating  the 
two  metal  surfaces.  When  this  is  done,  the  friction  is  that  of 
the  molecules  of  oil  against  one  another,  which  is  comparatively 
small.  If,  for  any  reason,  the  oil  film  is  broken,  the  molecular 
friction  of  the  lubricant  is  replaced  by  rubbing  friction  of  metal 
on  metal.  The  force  required  is  then  much  increased,  and  the 
work  done  appears  in  the  bearing  as  heat.  If  the  action  is 


J,  Journal;  B,  bearing  brass;   W,  wedge;  C,  oil  cellar. 

FIG.  3. — Standard  A.  E.  R.  E.  A.  Journal  and  Bearing. 

allowed  to  continue  for  any  great  time,  the  temperature  is 
raised  to  a  point  where  any  oily  waste  in  the  bearing  cellar 
will  catch  fire,  and  a  "hot-box"  results.  When  a  train  is 
standing  still,  the  static  pressure  of  the  bearing  on  the  journal 
will  squeeze  all  the  oil  out  from  between  the  bearing  surfaces,  so 
that  when  the  train  is  started  the  friction  is  quite  large.  As  the 
speed  increases,  oil  is  drawn  into  the  bearing,  and  the  friction 
reduced.  The  minimum  resistance  is  reached  at  a  speed  of 
about  30  miles  per  hr.  for  any  given  temperature  and  journal 
pressure;  and  beyond  this  point  it  becomes  greater  with  in- 
creased speed. 


THE  MECHANICS  OF  TRACTION  19 

Experiments  have  shown  that  the  friction  falls  as  the  pressure 
per  unit  area  is  increased,  within  the  ordinary  range  of  bearing 
pressures;  and  it  also  grows  less  with  rise  in  temperature  up  to 
the  point  where  the  viscosity  has  been  reduced  so  that  the  oil 
film  cannot  be  maintained.  This  is  beyond  the  ordinary  range  of 
working  temperatures. 

If  the  oil  is  too  fluid,  it  will  not  have  sufficient  viscosity  to  form 
a  film;  and  if  too  thick,  not  enough  will  be  drawn  into  the  bearing 
to  make  the  film  complete.  It  is  necessary  to  have  oil  of  the 
proper  viscosity  if  the  lubrication  is  to  be  good.  Since  the 
viscosity  varies  with  the  temperature,  a  heavier  oil  is  needed  in 
summer  than  in  winter.  Variations  in  the  character  of  the  oil 
used  will  cause  greater  differences  in  the  friction  than  any  of  the 
other  items  considered,  and  hence  it  is  not  possible  to  give  absolute 
figures  for  journal  friction  unless  the  characteristics  of  the  lubri- 
cant used  are  known. 

Flange  Friction,  Rolling  and  Oscillatory  Resistances. — These 
resistances  are  so  intermingled  that  no  attempt  to  separate  them 
has  been  successful.  The  causes  producing  one  of  them  usually 
gives  rise  to  the  others. 

Rolling  resistance  is  due  to  several  things.  The  loaded  wheel 
produces  a  deflection  of  the  rail,  and  also  compresses  it,  so  that 
in  effect  the  car  is  always  climbing  a  small  grade.  The  bending 
of  the  rail  is  augmented  by  deflections  and  compression  of  the 
ties  and  the  roadbed,  and  by  yielding  at  the  rail  joints. 

Flange  friction  is  produced  by  the  rubbing  of  the  wheel  flanges 
against  the  rail  heads.  This  varies  with  the  speed  of  the  train, 
condition  of  the  trucks,  shape  of  the  wheel  and  the  rail  and  other 
causes;  and  also  depends  to  some  extent  on  the  track  construction 
and  methods  of  suspension. 

Oscillatory  resistances  are  quite  indefinite.  If  the  train  sways 
from  side  to  side  of  the  track,  it  is  evident  that  a  certain  amount 
of  energy  must  be  absorbed  by  such  motion.  They  cannot  be 
determined  separately,  and  are  usually  considered  to  be  those 
resistances  remaining  after  the  other  items  have  been  accounted 
for.  They  are  necessarily  closely  related  to  the  rolling  friction. 
It  is  certain  that  they  increase  rapidly  with  the  speed,  since  the 
force  of  impact  varies  as  the  square  of  the  velocity. 

The  sum  of  the  flange  friction,  rolling  and  oscillatory  re- 
sistances make  up  a,  not  inconsiderable  portion  of  the  total  train 
resistance.  Although  the  above  discussion  would  indicate  that 


20 


THE  ELECTRIC  RAILWAY 


these  items  should  increase  more  rapidly  than  the  speed,  they  are 
considered  by  some  writers  to  vary  directly  with  it. 

Air  Resistance. — In  high-speed  operation  the  air  resistance  is 
the  most  important  factor  of  train  resistance.  This  may  be 
divided  into  three  components: 

1.  Head  end  resistance. 

2.  Side  friction. 

3.  Rear  suction. 

The  head  end  resistance  is  due  to  the  displacement  of  the  air 
caused  by  the  passage  of  the  train  through  it.  It  is  the  largest 


30  40  50 

Miles  per  Hour 

FIG.  4. — Head  end  air  resistance. 


20          30  40  50 

Miles  per  Hour 

FIG.  5. — Rear  end  air  suction. 


part  of  the  air  resistance.  It  depends  on  the  projected  area  of  the 
front  of  the  train,  the  shape  of  the  front,  and  the  speed.  A 
number  of  tests  have  been  made  to  quantitatively  determine  its 
value.  Prominent  among  these  are  the  ones  made  by  the 
Electric  Railway  Test  Commission,  formed  by  the  electric  railway 
interests  in  connection  with  the  Louisiana  Purchase  Exposition 
in  1904, 1  and  the  so-called  "  Berlin-Zossen "  tests,  conducted  in 

1  Report  of  the  Electric  Railway  Test  Commission,  McGraw  Publishing  Co., 
1906. 


THE  MECHANICS  OF  TRACTION  21 

1901  and  1902-03  by  a  committee  working  in  conjunction  with  the 
German  government1. 

The  conclusions  of  both  these  investigations  indicate  that  the 
head  end  air  resistance  varies  as  the  square  of  the  speed,  and  has 
materially  different  values  for  various  shapes  of  front  end.  The 
results  obtained  by  the  Electric  Railway  Test  Commission  are 
summarized  in  Fig.  4.  It  appears  that  a  wedge-shaped  front 
offers  much  less  resistance  than  the  ordinary  forms  used  on 
electric  cars. 

The  rear  suction  is  quite  similar  to  the  front  end  resistance, 
being  due  to  filling  the  partial  vacuum  formed  by  the  passage  of 
a  train  with  air  at  atmospheric  pressure.  It  follows  the  same 
laws,  but  is  less  in  amount,  than  the  front  end  resistance.  Values 
of  rear  suction  are  shown  in  Fig.  5.  It  may  be  noted  that  the 
resistance  of  the  parabolic  shaped  rear  end  is  less  than  that  of  the 
wedge,  which  at  the  front  end  gives  the  lowest  value. 

The  side  friction  is  caused  by  the  rubbing  of  the  air  against 
the  sides  of  the  car.  It  also  varies  approximately  as  the  square 
of  the  speed,  and  for  a  single  car  is  about  one-tenth  the  sum  of 
the  front  and  rear  resistances. 

Motor  and  Gearing  Friction. — In  the  case  of  electrically 
driven  cars,  there  is  a  certain  loss  due  to  the  friction  of  the  motor 
armature  bearings,  the  motor  axle  bearings,  and,  in  the  case  of 
geared  motors,  of  the  gears.  The  motor  bearing  friction  is 
ordinarily  included  in  the  losses  of  the  motor,  but  that  of  the 
axle  is  omitted.  It  follows  the  general  laws  of  friction,  as  in  that 
of  the  car  journals.  The  gear  friction  is  sometimes  included 
in  the  motor  losses,  and  in  others  must  be  taken  with  the  train 
resistance.  The  loss  incurred  in  the  transmission  of  power 
through  a  pair  of  spur  gears  such  as  are  commonly  used  in 
transferring  the  torque  from  the  armature  shaft  to  the  axle, 
generally  runs  between  3  per  cent,  and  9  per  cent.,  depending  on 
the  pitch  line  speed  and  the  condition  of  the  teeth.  New 
gears  show  a  higher  loss  than  those  which  have  worn  enough 
to  remove  the  irregularities  due  to  cutting.  The  loss  again 
increases  considerably  after  the  teeth  have  become  badly  worn. 
For  gears  in  good  condition  and  for  moderate  pitch  line  speeds, 
the  loss  is  about  3J^  per  cent,  of  the  power  transmitted. 

1  Berlin-Zossen  Electric  Railway  Tests  of  1902-03,  McGraw  Publishing 
Co.,  1905. 


22  THE  ELECTRIC  RAILWAY 

It  should  be  noted  that  the  losses  in  the  gears,  and  also  the 
mechanical  losses  in  the  motors,  while  supplied  electrically 
when  power  is  being  drawn  from  the  electric  circuit,  must  be 
taken  from  the  momentum  of  the  train  when  it  is  coasting. 
This  causes  some  difference  in  the  values  ef  train  resistance 
in  the  two  cases.  The  gear  loss  while  the  train  is  coasting  is,  how- 
ever, small,  since  the  power  transmitted  is  only  sufficient  to  drive 
the  armature  while  running  light.  In  case  the  motors  are  used 
for  any  form  of  dynamic  braking,  the  loss  will  of  course  be 
larger  in  proportion  to  the  power  drawn  from  them.  The  gear 
losses  occur  only  in  cars  and  locomotives  driven  by  motors 
acting  through  gearing,  being  of  course  entirely  absent  in  the 
case  of  gearless  machines. 

Determination  of  Train  Resistance. — A  number  of  methods 
have  been  employed  for  the  determination  of  the  resistance  of 
cars  and  trains,  the  practice  depending  to  some  extent  on  the 
motive  power  employed.  The  resistance  of  steam  trains  may 
be  obtained  by  any  one  of  three  methods.  The  first  of  these 
is  to  place  a  dynamometer  directly  behind  the  tender  of  the 
locomotive,  and  record  the  drawbar  pull.  This  pull,  if  obtained 
with  uniform  conditions  as  outlined  in  the  definition  at  the 
beginning  of  the  discussion,  is  a  direct  measure  of  the  resistance 
for  the  speed  at  which  the  observation  is  taken.  Results  deter- 
mined in  this  manner  are  inaccurate  in  that  the  head  end  re- 
sistance is  omitted.  In  the  case  of  long  freight  trains  operating 
at  relatively  slow  speeds,  this  is  unimportant;  but  with  high- 
speed passenger  trains  it  may  lead  to  considerable  error.  In 
steam  locomotive  work  the  inaccuracy  is  corrected  by  includ- 
ing the  head  end  resistance  in  the  "machine  friction"  of  the 
locomotive.  If  tests  made  in  this  way  are  to  be  used  for  deter- 
mining electric  train  resistance,  care  must  be  taken  in  interpret- 
ing them. 

The  second  method  of  obtaining  the  resistance  of  steam 
trains  consists  in  taking  indicator  diagrams  at  various  constant 
speeds,  and  from  the  cylinder  performance  determining  the  force 
supplied  to  overcome  train  resistance.  This  method  is  liable 
to  all  the  defects  encountered  when  indicating  steam  engines 
under  the  disadvantages  inherent  to  road  tests,  and  also  intro- 
duces an  error  by  including  the  locomotive  friction. 

The  third  method  consists  in  allowing  a  train  to  coast,  and 
finding  the  time  required  to  retard  from  one  given  speed  to 


THE  MECHANICS  OF  TRACTION  23 

another.  This  method  would  appear  to  be  of  at  least  as  great 
accuracy  as  the  last,  although  it  has  never  met  with  much  favor 
in  the  eyes  of  steam  railroad  men. 

The  resistance  of  electrically  equipped  trains  may  be  deter- 
mined readily  by  operating  at  constant  speed  under  the  proper 
conditions,  and  determining  the  input  to  the  motors.  If  the 
efficiency  of  the  motors  be  determined  by  a  separate  test,  the 
corresponding  output  can  be  found  at  once,  giving  the  value  of 
the  train  resistance  directly.  This  method  has  met  with  the 
greatest  favor  of  late  years,  and  the  best  and  most  consistent 
results  have  been  obtained  by  its  use. 

Train  Resistance  Formulae. — Ever  since  the  subject  of  train 
resistance  began  to  be  understood,  attempts  have  been  made  to 
render  the  results  of  tests  universally  applicable  by  presenting 
them  in  the  form  of  equations  involving  the  constants  of  the 
equipment  and  the  speed.  A  large  number  of  such  formulae  have 
been  published;  but  their  great  divergence  would  indicate  either 
that  they  are  inaccurate  or  that  they  are  inapplicable  over  a 
wide  range  of  conditions  of  operation.  Of  these  formulae  there 
are  two  distinct  types:  those  applying  to  steam  trains,  which 
omit  head  end  resistance,  and  those  applying  to  electric  trains, 
which  include  this  item.  Although  the  resistance  of  either 
kind  of  train  is  essentially  the  same  for  similar  conditions,  the 
above  difference  will  cause  considerable  variation  in  the  train  re- 
sistance equation.  Unfortunately,  investigators  do  not  always 
specify  the  class  of  trains  to  which  their  formulae  are  applicable. 

In  obtaining  a  rational  formula  for  train  resistance,  it  is  obvious 
that  several  of  the  components  can  be  grouped  together.  A 
portion  is  sensibly  constant  at  all  speeds,  a  part  varies  as  the 
speed,  and  still  another  as  its  square.  If  there  are  functions  of 
higher  powers  of  the  speed,  they  have  not  as  yet  been  segregated, 
and  they  must  be  quite  unimportant.  A  rational  train  resistance 
formula  should  then  be  of  the  type 

R  =  A  +  BV  +  C72  (20) 

where  R  is  the  resistance  in  pounds  per  ton,  V  the  speed  of  the 
train  in  miles  per  hour,  and  A,  B  and  C  coefficients  determined 
experimentally. 

A  formula  of  the  semi-rational  type  has  been  developed  by 
Mr.  A.  H.  Armstrong,  as  follows: 

(21) 


24 


THE  ELECTRIC  RAILWAY 


in  which  R  is  the  resistance  in  Ib.  per  ton, 
T  is  the  weight  of  the  train  in  tons, 
V  is  the  speed  of  the  train  in  miles  per  hr., 
a  is  the  area  of  cross-section  of  the  train  in  sq.  ft., 
n  is  the  number  of  cars  in  the  train. 

The  first  term  represents  largely  the  bearing  friction,  the 
second  the  rolling  resistance,  flange  friction  and  a  portion  of  the 
oscillatory  resistance,  and  the  third  term  the  remainder  of  the 
oscillatory  resistance  and  the  air  resistance.  The  last  factor 
of  the  third  term  is  to  allow  for  the  side  air  friction  if  there  be 
more  than  one  car  in  the  train.  This  formula  has  given  fairly 


30  40  50 

Speed,  Miles  per  Hour 

FIG.  6. — Train  resistance  for  cars  of  different  weights. 


consistent  results,  and  may  be  safely  used  in  predetermining  the 
train  resistance  for  ordinary  American  passenger  rolling  stock. 

In  Fig.  6  is  shown  the  application  of  Armstrong's  equation  for 
cars  of  different  weights.  The  curves  are  of  the  same  general 
type,  and  differ  only  in  the  first  and  third  terms.  In  Fig.  7  is 
shown  a  series  of  curves  for  the  resistance  of  different  trains  made 
up  of  cars  of  the  same  weight.  The  lower  resistance  per  ton  as 
the  number  of  cars  in  the  train  is  increased  is  clearly  shown. 

It  should  be  noted  that  none  of  the  formulae  for  train  resistance 
in  the  form  of  equation  (20)  make  allowance  for  the  starting 
resistance.  This  will  usually  be  much  greater  than  the  resistance 
after  even  a  very  low  speed  has  been  attained,  on  account  of  the 
high  bearing  friction  at  starting.  This  has  already  been  referred 


THE  MECHANICS  OF  TRACTION 


25 


to,  and  accounts  for  some  discrepancies  which  appear  in  the 
application  of  train  resistance  equations. 

It  is  more  difficult  to  determine  the  resistance  of  freight  trains 
than  that  of  passenger  trains,  since  the  former  are  made  up  of 


8. 

\n 

T5 

I 

•^ 

! 


10 


60 


70 


30          40  SO 

Speed,  M.P.H. 

FIG.  7. — Train  resistance  for  different  numbers  of  cars. 


80 


cars  of  widely  varying  weight  and  different  design.  There  is 
moreover  a  difference  in  resistance  between  that  found  for  loaded 
cars  and  for  empties.  The  expense  of  making  up  complete  trains 


10 


25 


30 


35 


40 


15  20 

Speed,  M.P.H. 
FIG.  8. — Freight  train  resistance. 

of  freight  cars  of  one  weight  and  type  would  be  great;  and  the  cost 
would  not  be  justified,  since  such  trains  are  not  to  be  found  in 
practice.  A  better  method  is  to  make  tests  on  ordinary  trains 


26 


THE  ELECTRIC  RAILWAY 


of  any  make-up,  and  base  the  resistance  on  the  average  car  weight. 
The  result  of  such  a  series  of  tests  on  trains  in  regular  service  is 
shown  in  Fig.  8,  which  is  from  results  obtained  by  Professor 
Edward  C.  Schmidt.1 

These  curves  were  taken  with  a  dynamometer  car,  and  do  not 
include  the  head  end  resistance. 

Incidental  Resistances.  Grades. — In  surmounting  a  grade  a 
train  has  to  be  lifted  through  a  definite  vertical  distance.  To  do 
this  a  certain  amount  of  force  is  required,  sufficient  to  balance  the 
tendency  of  the  train  to  run  down  the  grade.  The  measure  of  this 
is  the  value  of  the  gradient,  which  may  be  expressed  either  in 


FIG.  9.  —  Determination  of  grade  resistance. 

per  cent,  rise,  or  in  feet  rise  per  mile.  The  surveyor,  in  laying 
out  the  track,  measures  the  horizontal  distance,  I  (Fig.  9),  and  the 
vertical  height  h.  If  a  train  weighing  T  tons  be  on  the  grade, 
this  weight  may  be  resolved  into  two  components,  N  normal  to  the 
track  and  F  along  the  track.  It  is  this  latter  force  which  must  be 
balanced  by  the  force  Ff  to  keep  the  train  in  equilibrium.  The 
value  of  the  force  F  is  T  sin  a.  Since  N  and  T  are  respectively 
perpendicular  to  t  and  I,  and  angles  BCA  and  bca  are  right  angles, 
the  triangles  ABC  and  abc  are  similar,  and  angle  B  AC  =  angle 
bac.  Therefore, 

F'  =  -  F  =  T  sin  a  =  T  -  (22) 

L 

It   is   usually   inconvenient    to   determine  -   directly;   but   the 

* 

tangent  of  the  angle  a,  j,  may  be  readily  found.  For  ordinary 
grades  the  error  is  negligible  in  assuming  the  sine  equal  to  the 


C.  SCHMIDT,  "Freight  Train  Resistance,"  Bulletin  43,   Engi- 
neering Experiment  Station,  University  of  Illinois. 


THE  MECHANICS  OF  TRACTION  27 

tangent.  For  example,  the  error  for  a  4  per  cent,  grade,  which  is 
about  the  practical  limit,  is  one-fourth  of  1  per  cent.,  and  for  a 
10  per  cent,  grade,  one-half  of  1  per  cent. 

For  a  rise  of  1  ft.  per  100,  and  a  train  weight  of  1  ton, 

F  =  2000  X  ^  =  20  Ib.  (23) 


For  a  rise  of  1  ft.  per  mile,  and  a  weight  of  1  ton, 

F  =  2000  X  -^77  =  0.3788  Ib.  (24) 


The  force  necessary  to  maintain  motion  on  a  grade  is  there- 
fore 20  Ib.  per  ton  for  each  per  cent,  of  rise,  or  0.3788  Ib.  per 
ton  for  each  foot  per  mile.  If  the  train  is  going  down  the  grade, 
the  force  is  in  the  opposite  direction,  and  aids  the  tractive  effort 
of  the  motive  power. 

Virtual  Grades.  —  When  the  speed  of  a  train  is  changing,  it 
may  be  considered  that  it  is  virtually  on  a  slope  whose  resistance 
is  equal  to  the  sum  of  the  resistance  of  the  actual  grade  and 
that  of  one  which  is  equivalent  in  its  effect  to  the  acceleration. 
A  grade  of  this  character  is  called  a  "  virtual"  or  "velocity" 
grade,  and  the  total  resistance  of  a  train  on  it  is  always  equal  to 
that  on  the  actual  grade  and  the  resistance  corresponding  to 
the  force  required  for  acceleration.  The  virtual  grade  may 
be  either  greater  or  less  than  the  actual  one,  depending  on  whether 
the  train  speed  is  increasing  or  decreasing;  or,  in  other  words, 
whether  the  acceleration  is  positive  or  negative. 

When  trains,  especially  those  making  infrequent  stops,  such 
as  heavy  freight  trains,  are  operated  on  roads  having  a  broken 
profile,  it  is  often  possible  to  approach  the  up-grades  at  higher 
speeds  than  can  be  maintained  to  the  summit.  The  stored 
kinetic  energy  will  be  reduced  as  the  ascent  progresses,  and  be 
liberated.  This  energy  will  aid  in  lifting  the  train,  thus  being 
converted  into  potential  energy.  In  effect,  the  resistance 
will  be  less  than  that  due  to  the  actual  grade;  and,  in  deter- 
mining the  weight  of  train  that  can  be  hauled  by  a  given  loco- 
motive, the  virtual  grade  should  preferably  be  used.  It  is  then 
important  to  find  the  value  of  the  latter,  which  may  readily  be 
done  by  calculating  the  liberated  kinetic  energy  due  to  the 
difference  in  speeds  between  that  of  approach  and  at  the  summit. 
The  length  of  the  grade  being  known,  the  average  velocity  dur- 


28  THE  ELECTRIC  RAILWAY 

ing  ascent  can  be  found,  and  the  force  equivalent  to  the  con- 
verted energy  determined.  This  force,  subtracted  from  the  re- 
sistance of  the  actual  grade,  gives  that  corresponding  to  the 
virtual  grade.  From  this  the  resistance  in  pounds  per  ton,  and 
the  equivalent  rise  in  feet  per  mile  or  in  per  cent,  may  be  found 
directly  by  equations  (23)  or  (24).  It  is  evident  that  virtual 
grades  are  always  limited  in  length. 

The  Ruling  Grade.  —  In  any  given  section  of  track,  the  maxi- 
mum gradient  encountered  is  known  as  the  "  ruling  grade," 
whether  it  be  an  actual  or  a  virtual  one.  The  maximum  load 
which  a  given  motive  power  can  haul  on  a  certain  division  of  a 
road  is  determined  by  the  greatest  tractive  effort  it  can  exert  on 
the  ruling  grade.  In  general,  ruling  grades  are  not  of  such  great 
importance  in  the  case  of  electric  roads  as  in  steam  roads,  since 
the  electric  motors  can  usually  be  forced  beyond  their  normal 
rating  for  a  short  time,  as  in  climbing  the  ruling  grade;  whereas 
the  maximum  output  of  the  steam  locomotive  is  practically  a 
fixed  quantity,  which  cannot  be  exceeded  for  even  a  short 
period. 

Curves.  —  In  American  railway  practice  it  is  customary  to 
rate  curves  in  degrees  of  central  angle  subtended  by  a  chord  of 
100  ft.  This  method  follows  from  the  ordinary  procedure  in 
laying  out  curves  with  a  transit.  At  the  point  of  curvature,  A, 
Fig.  10,  the  instrument  is  set  up,  and  angles  DAB,  FAC,  etc., 
laid  off,  each  equal  to  one-half  the  "degree"  of  the  curve. 
In  the  case  of  a  1°  curve,  the  angle  A  OB  is  1°  and  DAB  is 
0°  30'.  Referring  to  Fig.  10,  if  AB  =  100  ft.,  then 

AK         .    a  /0_, 

AO    =  Sm  2  (25) 

=  sin  0°  30'  =  0.00873, 


from  which  AO  =  5730  ft.     In  general,  if  D  is  the  degree  of  the 
curve,  and  r  its  radius, 

sin  y2  D  =  ~  (26) 

and 

r  =  50  esc  %  D  (26a) 

Approximately,  the  radius  for  ordinary  curves  may  be  taken  as 
~~f\~  ft.     In  curves  of  large  degree  and  correspondingly  small 


THE  MECHANICS  OF  TRACTION 


29 


radius  this  assumption  leads  to  considerable  error;  and  when 
laying  them  out  chords  of  50  ft.  or  less  are  used  in  place  of  the 
100  ft.  which  is  employed  for  those  of  longer  radius.  In  street 
railway  work,  where  the  radii  are  extremely  short,  being  from 
35  ft.  to  100  ft.,  the  curves  are  ordinarily  designated  by  the 
radius  in  feet.  In  such  cases  they  are  not  usually  laid  out  with 
instruments;  but  the  rails  are  shaped  and  assembled  by  the 
manufacturer  before  shipment  and  are  installed  as  a  complete 
unit.  Such  track  is  referred  to  under  the  general  term  "special 
work." 


FIG.  10. — Method  of  laying  out  curves. 

In  high-speed  railway  work  an  abrupt  change  of  direction  from 
a  tangent  to  a  circular  curve  would  cause  difficulty  in  operation, 
and  might  even  make  a  train  leave  the  track.  To  obviate  this 
difficulty  the  first  portion  of  a  curve  is  some  form  of  spiral  which 
makes  an  easy  transition  from  the  tangent  to  the  circular  arc. 
A  number  of  such  curves  are  in  use  and  methods  of  construction 
may  be  found  in  any  good  handbook  on  railway  location. 

Since  a  body  in  motion  tends  to  travel  in  a  straight  line,  a 
force  must  be  introduced  in  order  to  cause  it  to  change  its  direction. 
The  value  of  this  force  depends  on  the  speed  and  weight  of  the 
train  and  the  amount  of  curvature;  it  may  be  supplied  by  pres- 


30 


THE  ELECTRIC  RAILWAY 


sure  of  the  wheel  flanges  against  the  outer  rail  of  the  track  or  by 
gravity.  In  the  latter  case  the  force  is  obtained  by  locating  the 
outer  rail  of  the  track  at  a  higher  level  than  the  inner.  This  is 
known  as  the  superelevation  of  the  outer  rail. 

In  Fig.  11  consider  a  car  of  weight  G  =  Mg  on  a  curve  of  radius 
r,  the  superelevation  of  the  outer  rail  being  such  that  the  track 
makes  an  angle  <j>  with  the  horizontal.  The  force  G  due  to  the 
weight  of  the  car  will  have  a  tendency  to  pull  the  train  toward  the 

center  of  the  curve.     The  centrifugal  force  has  a  value  of  - 


FIG.   11. — Centrifugal  effect  of  curves. 

exerted  in  a  horizontal  direction.     From  the  figure  it  may  be  seen 
that  the  resultant  of  these  forces  will  be  normal  to  the  track  when 


tan  0  =  - 
rg 


(27) 


It  is  evident  from  the  above  discussion  that  the  superelevation 
of  a  curve  is  correct  for  one  speed,  and  for  that  speed  only.  If  the 
velocity  be  greater  than  this  value,  the  reaction  from  the  track 
will  not  supply  all  of  the  directive  force  required;  the  remainder 
must  be  furnished  by  pressure  of  the  flanges  against  the  outer 
rail;  if  less  than  the  balancing  speed,  the  force  supplied  by  the 
track  reaction  will  be  greater  than  necessary,  and  the  train  will 
fall  toward  the  inner  rail,  the  pressure  being  taken  by  the  flanges 
of  the  inner  wheels.  In  either  of  these  cases  there  will  be  an 
amount  of  flange  friction  additional  to  that  occurring  on  straight 
track. 

Since  the  tracks  of  ordinary  railroads  must  be  used  in  common 
by  fast  and  by  slow  trains,  it  is  not  possible  to  compensate  the 
curves  for  all  of  them.  A  compromise  is  usually  effected  so  that 


THE  MECHANICS  OF  TRACTION  31 

the  superelevation  is  too  great  for  the  freight  trains  and  too  small 
for  the  passenger  trains.  The  general  result  will  be  to  reduce  the 
resistance  on  curves  for  all  of  them,  and  to  make  operation  safe 
at  speeds  up  to  the  maximum  used.  The  proper  choice  of  a  mean 
velocity  for  which  the  compensation  should  be  calculated  depends 
on  the  relation  between  the  speeds  of  different  classes  of  trains 
and  the  relative  numbers  operated. 

A  certain  amount  of  friction  is  also  present  due  to  swinging 
the  trucks  from  their  normal  position  under  the  cars.  The  total 
effect  is  to  increase  the  train  resistance.  Experiments  indicate 
that  this  increase  in  train  resistance  averages  from  0.5  Ib.  to  1.5  Ib. 
per  ton  per  degree  of  curvature. 

Wind  Resistance. — Natural  winds  a#ect  the  operation  of  trains 
by  changing  the  relative  velocity  of  the  train  with  respect  to  the 
air,  and  hence  vary  the  air  resistance.  For  example,  a  train 
operating  at  40  miles  per  hr.  against  a  head  wind  blowing  at  the 
rate  of  20  miles  per  hr.  will  have  the  same  wind  resistance  as 
though  it  were  moving  through  still  air  at  60  miles  per  hr.  If 
operating  in  the  opposite  direction  (i.e.,  with  the  wind)  the  effect 
will  be  the  same  as  the  air  resistance  met  by  moving  through  still 
air  at  20  miles  per  hr.  Quartering  and  side  winds  also  affect 
train  resistance  by  introducing  additional  flange  friction,  the 
wheels  being  crowded  against  the  rails  on  the  "  lee  ward"  side. 
In  general  these  results  are  indeterminate  in  amount. 

The  Speed-Time  Curve. — In  order  to  make  a  rational  com- 
parison of  train  performance  under  varying  conditions  of  opera- 
tion it  is  necessary  to  adopt  some  standard  method  of  reporting 
results.  This  need  has  led  to  the  use  of  a  series  of  curves,  all 
plotted  with  time  as  their  abscissae.  The  ordinates  of  this  group 
of  curves  may  be  any  of  the  factors  which  vary  with  the  time,  and 
include  the  distance  covered,  the  speed,  the  acceleration,  the 
tractive  effort,  and  the  electrical  quantities  current,  e.m.f.  and 
power.  Of  the  mechanical  values,  distance  is  the  fundamental 
one;  in  the  equations  at  the  beginning  of  this  chapter  some  of 
those  which  depend  on  the  distance  are  derived.  It  is  seen  that 
velocity  is  the  rate  of  change  of  distance  with  respect  to  time,  or 

ds 

v  =  dt  (4) 

Acceleration  is  the  rate  of  change  of  velocity  with  respect  to 
time,  or 


32  THE  ELECTRIC  RAILWAY 

«-*  (28) 

From  the  relations  of  these  two  equations  it  may  be  seen  that  ac- 
celeration is  the  second  derivative  of  the  distance  with  respect  to 
time,  or 

a  =  J  (29) 

In  certain  problems  involving  excessive  acceleration  and 
retardation,  it  has  been  found  that  a  high  rate  of  change  of 
velocity  can  be  maintained  without  discomfort  if  it  is  reached 
gradually.  This  brings  into  use  the  rate  of  change  of  the  ac- 
celeration, giving  the  relation 

da        d2v        d*s 

w  ::  w  ""  w 

In  a  similar  manner,  the  velocity  is  the  first  integral  of  the 
acceleration,  as 

v  =  fadt  (31) 

The  distance  is  the  first  integral  of  the  velocity,  and  the  second 
integral  of  the  acceleration. 

s  =  fvdt  =  f  fadt  (32) 

The  use  of  graphical  methods  for  the  representation  of  train 
motion  brings  in  these  relations,  and  the  performance  may  be 
shown  by  means  of  the  distance-time,  speed-time,  or  accelera- 
tion-time curves,  as  desired.  If  a  distance-time  curve  be  dif- 
ferentiated with  respect  to  time,  the  first  differential  curve  will 
be  that  between  speed  and  time,  and  the  second  differential 
curve  that  between  acceleration  and  time.  Similarly,  the  first 
integral  curve  of  the  acceleration-time  curve  is  the  speed-time 
curve,  and  the  second  integral  curve  the  distance— time  curve. 
If  any  one  of  the  three  curves  be  plotted,  it  is  a  simple  matter 
to  derive  the  other  two.  Since  the  area  enclosed  between  a 
curve  and  its  axis  of  abscissae  is  a  measure  of  the  integral,  a 
fairly  definite  idea  of  that  value  may  be  found  by  inspection. 
In  like  manner,  the  slope  of  a  curve  is  a  measure  of  its  derivative, 
and  the  general  form  of  the  differential  curve  may  be  approxi- 
mated. For  this  reason,  more  information  can  be  obtained 
by  the  use  of  the  speed-time  curve  than  by  employing  either 
the  distance-time  curve  or  the  acceleration-time  curve  for  depict- 
ing the  motion  of  a  train. 


THE  MECHANICS  OF  TRACTION  33 

Components  of  the  Speed-Time  Curve. — In  ordinary  railway 
operation,  a  train  starts  from  rest,  and  its  speed  is  increased 
with  a  rapid  acceleration,  which  will  usually  fall  off  as  the 
speed  is  increased,  until  the  train  operates  at  constant  speed. 
The  train  may  then  be  allowed  to  coast  without  the  use  of 
power,  after  which  it  is  stopped  rapidly  by  application  of  the 
brakes. 

Acceleration  Curve. — In  order  to  produce  motion,  a  certain 
force  must  be  used,  which  can  be  calculated  quantitatively  if 
the  weight  of  the  train  and  the  required  acceleration  are  known; 
or  the  acceleration  can  be  determined  if  the  force  and  the 
train  weight  are  given.  The  method  of  calculation  is  that 
indicated  by  equations  (12)  and  (19).  If  the  force  remains 
constant,  the  train  will  be  accelerated  at  a  uniform  rate;  but  if 
the  force  is  variable,  the  acceleration  will  fluctuate  correspond- 
ingly. If  the  law  of  variation  of  the  accelerating  force  (tractive 
effort)  can  be  stated  in  the  form  of  an  equation,  then  the  resulting 
acceleration  and  the  speed  at  any  instant  can  be  determined 
analytically.  Ordinarily,  the  relation  between  tractive  effort 
and  time  is  so  intricate  that  no  exact  expression  for  it  can  be 
found.  In  any  case  it  is  too  complex  for  easy  mathematical 
analysis.  Recourse  is  usually  had  to  a  graphical  method  of 
treatment,  which  facilitates  the  calculation  materially. 

As  the  speed  of  the  train  increases,  the  train  resistance  be- 
comes greater,  while  at  the  same  time  the  tractive  effort,  as 
supplied  by  nearly  all  motive  powers,  diminishes.  A  speed  will 
be  reached  where  the  train  resistance  will  have  increased  to  a 
point  where  it  just  equals  the  tractive  effort.  It  is  evident 
that  there  can  then  be  no  further  acceleration,  and  that  the 
speed  must  become  constant  at  this  limiting  value.  This  is 
often  referred  to  as  the  "  balancing  speed."  It  is  always  the 
same  for  constant  conditions,  but  varies  with  the  grade  and  the 
other  incidental  resistances  which  may  occur.  The  train  will 
continue  to  run  at  this  speed  until  the  conditions  change,  or  until 
power  is  cut  off. 

Coasting  Curve. — When  no  power  is  supplied  to  the  moving 
train,  it  will  continue  in  motion,  but  will  be  retarded  at  a  rate 
which  depends  on  the  value  of  the  train  resistance.  This  re- 
tardation becomes  less  as  the  speed  decreases,  since  the  train 
resistance  diminishes  with  reduction  in  speed.  In  case  the  train 
is  on  a  down  grade  which  gives  a  force  great  enough  to  equal  or 


34  THE  ELECTRIC  RAILWAY 

exceed  the  train  resistance,  the  train  will  coast  at  constant  or  even 
increasing  speed. 

Braking  Curve. — To  stop  a  train  by  allowing  it  to  coast  to  a 
standstill  would  be  impractical,  and  in  some  cases  impossible; 
hence  a  retarding  force  additional  to  the  train  resistance  must  be 
introduced  to  cause  more  rapid  stopping.  This  force  is  ordinarily 
supplied  by  some  form  of  brake.  In  ordinary  railway  practice 
the  force  supplied  is  due  to  the  friction  of  metallic  shoes  pressing 
against  the  treads  of  the  wheels,  although  other  methods  are 
sometimes  employed.  A  discussion  of  this  topic  is  given  in 
Chapter  VII. 

The  dynamic  relations  while  braking  are  precisely  the  same  as 
those  existing  during  acceleration,  except  that  the  main  force  is 
reversed  in  direction.  The  acceleration  is  therefore  negative. 
Its  value  may  be  determined  quantitatively  by  the  applica- 
tion of  the  same  equations  as  used  for  a  consideration  of  ac- 
celeration, care  being  taken  that  the  algebraic  signs  are  correctly 
interpreted. 

Calculation  of  Speed-Time  Curves. — The  problem  of  plotting 
the  speed-time  curve  from  given  data  is  one  which  is  constantly 
recurring  in  railway  work;  and  it  is  desirable  to  have  at  hand  a 
simple  and  accurate  means  of  making  the  determination.  An 
inspection  of  equations  (28)  to  (32)  gives  the  basis  of  the  method 
available  for  making  the  calculation. 

The  most  convenient  way  of  determining  the  graphical  repre- 
sentation of  the  speed-time  relation  is  to  locate  points  on  a  sheet 
of  coordinate  paper  for  a  number  of  values  lying  along  the  curve, 
these  points  being  taken  sufficiently  close  together  to  give  the 
required  accuracy,  and  the  curve  plotted  through  them.  The 
closer  they  are  taken  together,  the  more  accurate  is  the  curve. 
The  data  given  in  the  statement  of  the  problem  usually  are  the 
tractive  effort  and  the  speed  to  which  it  corresponds.  In  other 
words,  the  information  is  that  derived  from  the  characteristic 
curve  of  the  motive  power,  such  as  the  curve  of  the  series  railway 
motor,  Fig.  19.  From  equations  (13),  (19)  or  (19a)  the  accelera- 
tion produced  by  the  motor  tractive  effort  may  be  found  at  once. 
This  gives  us  the  speed  and  the  corresponding  value  of  accelera- 
tion, from  which  the  time  must  be  calculated.  The  means  of 
doing  this  is  to  use  the  relation 

a  -  *  (28) 


THE  MECHANICS  OF  TRACTION 


35 


which  may  be  rewritten 


*-* 

a 


(28a) 


This  shows  at  once  that  there  is  no  easy  way  of  getting  the 
summation  of  the  time  increments  for  a  given  run,  since  it  is  not 
possible  to  have  a  simple  equation  expressing  the  relation  between 
speed  and  tractive  effort  of  the  motive  power.  The  total  elapsed 
time  from  any  reference  point  must  be  the  summation  of  a  large 
number  of  increments;  and  the  result  obtained  depends  to  a 
large  extent  on  the  accuracy  of  the  method  employed  for  de- 
termining the  successive  time  increments.  Any  graphical 
method  for  plotting  speed-time  curves  thus  consists  of  approxi- 
mating the  value  of  time  corresponding  to  a  definite  acceleration. 


FIG.  12. — Determination  of  time  increments. 

In  this  figure  the  increments  dy  and  dx  are  assumed  to  be  infinitesimal. 

Mr.  C.  O.  Mailloux1  has  resolved  the  problem  into  the  follow- 
ing form :  "  Given  the  ordinate,  y,  and  the  slope  of  the  curve,  '-p, 

at  any  point  of  a  curve,  to  find  the  abscissa,  x,  corresponding  to 
the  ordinate,  or  the  distance  of  the  ordinate  from  the  F-axis." 
Two  cases  exist — the  first  where  the  slope  is  positive,  comprising 
all  acceleration  curves;  and  the  second  where  the  slope  is  negative, 
which  includes  all  retardation  curves.  In  the  former  case  the 
curves  are  usually  concave  to  the  X-axis,  and  in  the  latter  may  be 
either  concave  or  convex  to  it. 

In  Fig.  12  the  curve  OEF  represents  any  portion  of  a  speed-time 

1C.  O.  MAILLOUX,  "Notes  on  the  Plotting  of  Speed- Time  Curves," 
Transactions  A.  I.  E.  E.,  Vol.  XIX,  p.  984  (1902).  The  following  discussion 
is  based  on  this  paper. 


36  THE  ELECTRIC  RAILWAY 

curve  with  a  positive  slope  (i.e.,  an  acceleration  curve).  Consider 
lines  drawn  tangent  to  the  curve  at  various  points,  as  ab,  cd,  ef. 
Also  take  two  ordinates  y  and  y',  which  are  very  close  together, 
and  which  may  be  assumed  to  include  the  portion  of  the  speed- 
time  curve  at  the  point  of  tangency,  E,  of  the  line  cd.  The 
difference  between  these  is  dy,  and  we  may  write 

dy  =  y'  -  y  (33) 

The  corresponding  difference  between  the  abscissae,  dx, 
is 

dx  =  x'  -  x  (34) 

In  order  that  the  two  ordinates  may  be  considered  to  be  at  the 
same  point  of  tangency,  E,  the  distance  between  them  must  be 
infinitely  small. 

The  application  of  similar  triangles  to  Fig.  12  gives  the  relation 

^  =  d/  (35) 

cx       dx 

which  expresses  the  well-known  fact  that  the  ordinate  y  at 
the  point  of  tangency,  divided  by  the  sub-tangent  cx,  is  a 
measure  of  the  differential  at  that  point.  From  this  relation  the 

value  of  -/  can  be  determined. 
ax 

The  assumption  that  has  been  made,  that  the  increment  of 
ordinate,  dy,  is  infinitesimal,  makes  it  of  no  value  in  the  plotting 
of  curves.  For  ordinary  purposes  it  must  be  increased  to  some 
finite  value.  This  makes  necessary  a  re-statement  of  equa- 
tions (33)  and  (34)  as  follows  (see  Fig.  13) : 

x'  -  x  =  Ax  (36) 

y'  -  y  =  by  (37) 

in  which  Ai/  is  the  increment  of  ordinate  which  corresponds 
to  the  increment  of  abscissa  Ax. 

The  essential  difference  between  the  infinitesimal  and  the 
finite  statements,  as  given  in  equations  (33)  and  (34),  and  (36) 
and  (37),  is  that  while  in  the  former  case  the  ordinates  are 
taken  so  close  together  that  there  is  no  appreciable  difference  in 

dy 
the  values  of  -/-  whether  measured  by  the  tangent  at  the  point 

of  the  curve  having  the  ordinate  y,  or  that  with  the  ordinate 
y',  it  may  not  hold  true  in  the  latter.  This  is  shown  in  Fig.  13, 


THE  MECHANICS  OF  TRACTION 


37 


which  is  purposely  exaggerated.     At  the  point  E,  the  differential 
is 

dy  =    V_ 

dx  ex 
while  at  the  point  F  it  is 

dy'  j/_ 

dx'  '   ex' 


(38) 


(39) 


It  may  thus  be  seen  that  the  differential  coefficient  cannot  be 
represented  by  any  single  value  when  the  increment  of  ordinate 
is  large  enough  that  a  material  change  in  the  slope  of  the  curve 
is  included. 

The  correct  value  of  the  differential  coefficient  will,  in  general, 
correspond  to  some  intermediate  point,  such  as  D.     Drawing 


c 


FIG.   13.  —  Practical  method  for  estimating  acceleration. 

In  this  figure  the  speed  increment.  Ay,  and  the  corresponding  time  increment,  Ax,  are 
taken  as  finite  values.      Compare  with  Fig.  12. 

the  line  gh  parallel  to  the  tangent  g'h'  through  this  point,  the 
differential  triangle  EFH  is  produced,  which  is  similar  to  the 
differential  triangle  corresponding  to  the  point  D.  We  can 
therefore  write 


dx0 


(40) 


where  XQ,  y0,  are  the  coordinates  of  the  point  D. 

An  inspection  of  the  triangles  EmI,  EFH  and  EnJ  shows  the 
difference  in  the  magnitude  of  Arc  as  obtained  when  using  the 
values  of  differential  corresponding  to  x,  XQ  and  x',  respectively. 
In  a  majority  of  curves,  the  point  D  is  approximately  midway 
between  E  and  F.  When  y  and  y'  are  taken  sufficiently  close 


38  THE  ELECTRIC  RAILWAY 

together,  the  error  made  by  assuming  this  condition  to  be  true 
becomes  negligible.  The  value  of  the  differential  may  then  be 
taken  as  that  corresponding  to  the  average  point  between  those 
of  y  and  y',  so  that 

V"  =  -^/  (41) 

The  closer  the  values  of  y  and  y'  are  taken  together,  the  smaller 
will  be  the  error  introduced  by  making  this  approximation. 

Total  Force  for  Train  Operation. — A  study  of  the  foregoing 
paragraphs  indicates  that  a  number  of  forces  are  always  pres- 
ent, which  govern  the  total  amount  of  power  which  must  be 
supplied  to  the  moving  train.  If  a  train  is  moving  at  constant 
speed  through  still  air  on  a  straight  level  track,  the  only  force 
required  is  that  to  overcome  the  normal  train  resistance;  but 
if  it  is  on  a  grade,  or  on  a  curve,  or  in  the  presence  of  a  natural 
wind,  a  variation  in  the  force  becomes  necessary  if  the  train  is 
to  maintain  its  speed.  If  the  speed  of  the  train  is  changing,  still 
other  forces  act. 

The  laws  of  motion  show  that  the  resultant  of  all  forces  act- 
ing on  a  body  is  their  algebraic  or  vector  sum.     Since  all  the 
forces  which  concern  the  movement  of  trains  act  parallel  to 
the  track,  the  algebraic  sum  gives  a  correct  representation  of 
the  total.     Using  the  following  notation: 
R  =  force  for  overcoming  train  resistance, 
G  =  force  for  overcoming  (up)  grades, 
C  =  force  for  overcoming  curves, 
P  =  force  for  producing  (positive)  acceleration, 
F  =  total  force  to  be  supplied  by  the  motive  power, 
we  may  then  state  as  an  equation  the  value  of  total  force 

F  =  R  ±G  +  C  ±P  (42) 

In  this  statement  the  value  of  P  must  be  taken  to  include  both 
force  for  linear  and  for  rotational  acceleration.  The  value  of  G 
is  positive  on  up  grades,  since  it  acts  as  a  resistance,  or  opposes 
the  force  F'}  on  down  grades  it  is  negative.  The  value  of  P 
is  positive  when  the  speed  is  increasing  (i.e.,  when  the  accelera- 
tion is  positive),  and  becomes  negative  when  the  speed  is  de- 
creasing from  any  cause.  In  other  words,  the  kinetic  energy 
increases  directly  with  the  (square  of)  speed. 

At  the  end  of  every  practical  run,  it  is  necessary  to  bring  the 
train  to  rest  by  the  application  of  an  external  retarding  force. 


THE  MECHANICS  OF  TRACTION  39 

This  phenomenon  is  known  as  braking,  and  will  be  taken  up  in 
detail  in  a  later  chapter.  The  necessary  value  of  braking  force 
may,  however,  be  determined  by  an  equation  similar  to  the  one 
above.  Using  the  same  notation,  and  calling  the  external  brak- 
ing force  B,  we  have, 

B  =  - R  +  G - C  +P  (43) 

It  is  to  be  noted  that  the  signs  of  R,  G  and  C  are  reversed; 
during  retardation  these  resistances  hasten  the  change  of  velocity. 
P  is  always  positive,  i.e.,  the  change  in  motion  is  always  in  the 
same  direction  as  the  retarding  force,  in  normal  braking. 

Plotting  Speed-Time  Curves. — The  relations  outlined  above 
give  a  practical  method  of  plotting  speed-time  curves.  The 
arrangement  involving  the  least  complication  is  to  make  an 
analytical  calculation  of  the  time  increments  (Az),  assuming 
speed  increments  (Ai/)  sufficiently  close  together  to  keep  the 
error  within  the  required  limits.  The  accuracy  will  depend  on 
the  conditions  of  the  individual  problem,  so  that  no  definite 
limits  for  the  speed  increments  can  be  stated.  It  must  be  re- 
membered that  the  calculations  are  somewhat  tedious,  and  need 
considerable  care,  to  prevent  inaccuracy.  Since  the  time  incre- 
ments must  be  added  together  to  give  the  total  time,  the  errors 
are  likely  to  be  cumulative,  and  cannot  be  expected  to  annul  one 
another. 

In  the  practical  calculation,  the  tractive  effort  curve  of  the 
motor  is  used  to  get  the  values  of  acceleration  corresponding  to 
various  speeds.  From  this  the  average  acceleration  during  the 
increment  is  found,  and  from  it  the  time  increment.  The  total 
elapsed  time  is  obtained  by  adding  together  these  latter. 

To  reduce  the  labor  incident  to  a  large  number  of  such  calcula- 
tions, several  methods  have  been  advanced  to  determine  the 
speed-time  curve  graphically.  Of  these,  the  one  most  used  is  that 
proposed  by  Mailloux.1  In  his  method  the  tractive  effort  of  the 
motor  is  replaced  by  the  acceleration  which  it  will  produce  on  th© 
given  equipment,  and  is  plotted  against  speed,  as  shown  in  Fig.  14. 
This  is  termed  the  "  gross  acceleration."  The  "net  acceleration," 
which  is  the  one  actually  produced  on  the  train,  is  determined  by 
subtracting  the  equivalent  negative  acceleration  due  to  the  train 
resistance.  This  is  the  result  on  straight  level  track.  When 

1  C.  O.  MAILLOUX,  "Notes  on  the  Plotting  of  Speed-Time  Curves," 
Transactions  A.  I.  E.  E.,  Vol.  XIX,  p.  984  (1902). 


40 


THE  ELECTRIC  RAILWAY 


grades  are  encountered,  a  constant  force  is  introduced,  amounting 
to  20  Ib.  per  ton  for  each  per  cent,  of  grade.  It  is  evident  that 
the  ordinate  of  the  net  acceleration  curve  will  be  increased  or 
diminished  by  the  corresponding  amount,  as  shown  by  the 
figures  at  the  right  of  the  chart.  This  has  the  effect  of  raising  or 
lowering  the  base  line  to  the  place  indicated  by  the  value  of 
grade.  Curves  may  be  similarly  treated,  except  that  their 
effect  is  always  opposed  to  the  direction  of  motion. 

Having  determined  the  acceleration  at  any  particular  speed 
from  a  chart  similar  to  Fig.  14,  the  corresponding  time  increment 
may  be  found  from  equation  (28o),  which  may  be  re-stated 


-»1 

a 


(286) 


2.0 


!  ° 


40      i 
Sjjeed  ,  Miles  per  Hour 

FIG.  14. — Chart  of  accelerations. 


This  normally  involves  the  calculation  of  -;  but  if  a  curve  is 

plotted  between  natural  numbers  and  their  reciprocals,  the 
values  of  a  may  be  taken  from  the  chart  of  accelerations  with 
dividers,  or  by  other  convenient  methods,  and  the  corresponding 

result  for  -  read  from  the  reciprocal  chart.  If  the  speed  incre- 
ment is  unity,  it  is  evident  that  the  time  will  be  given  directly 


THE  MECHANICS  OF  TRACTION  41 

by  this  method.  If  it  is  desired  to  use  other  speed  increments,  a 
series  of  curves  may  be  drawn  between  natural  numbers  and  one- 
half,  one-tenth,  twice,  ten  times,  etc.,  the  actual  values  of  recip- 
rocals. With  such  a  chart  the  determination  of  the  speed-time 
curve  is  relatively  quite  simple,  and  the  detailed  calculations  are 
all  dispensed  with.  It  is  evident  that  a  new  curve  of  accelera- 
tions must  be  made  for  each  different  motor,  or  for  the  same  motor 
with  different  equipments;  while  the  chart  of  reciprocals  is  equally 
good  for  all  cases. 

Power  for  Train  Movement.  —  Having  determined  the  force 
necessary  for  train  propulsion,  as  in  equation  (42),  it  is  easy  to 
calculate  the  power  required  at  any  instant  if  the  speed  be 
known.  This  is,  in  horsepower, 

HP  =  (44) 


where  F  is  the  total  tractive  effort  in  pounds,  and  v  the  speed 
in  feet  per  second.  If  the  speed  is  stated  in  miles  per  hour,  F,  the 
equation  becomes 

UD          5280  ffF  ,.  .  . 

HP  =  60X33,000  (44a) 

To  express  the  power  in  kilowatts,  we  have 

KW  = 


where  F  is  in  pounds  and  v  in  feet  per  second.  Using  speed  in 

miles  per  hour,  this  reduces  to 

_           5280^7  ,._  , 

KW  =  60  X  44,256.7  (45a) 


CHAPTER  III 
MOTORS  FOR  TRACTION 

Functions  of  Motive  Powers. — Any  motive  power  for  railway 
service  has  two  definite  functions: 

1.  To  accelerate  a  train  from  rest. 

2.  To  maintain  it  in  motion  at  a  predetermined  speed. 

These  functions  may  be  performed  by  almost  any  form  of 
electric  motor  now  known;  but  a  few  types  possess  inherent 
characteristics  so  much  better  suited  to  the  purpose  than  the 
others  that  they  are  used  almost  exclusively. 

Electric  Distribution  Systems. — Electrical  apparatus  is  usu- 
ally operated  on  one  of  two  well-defined  systems:  the  constant- 
current  or  the  constant-potential.  Although  it  is  not  im- 
possible to  operate  motors  on  a  moving  vehicle  from  a  constant- 
current  supply,  the  difficulties  are  so  great  that  after  a  few 
trials  it  has  been  entirely  abandoned  for  this  service.  The 
constant-potential  system,  on  the  other  hand,  readily  lends  it- 
self to  the  purpose  of  distributing,  energy  in  large  or  small 
amounts,  and  is  especially  adapted  for  serving  moving  cars  or 
locomotives.  Its  use  has  been  so  very  successful  that  at  the 
present  time  it  is  the  only  system  of  distribution  employed 
on  electric  railways.  The  entire  discussion  of  electrical  equip- 
ment in  this  book  will  be  confined  to  a  consideration  of  constant- 
potential  systems. 

The  systems  for  supply  of  electrical  energy  may  be  further 
classified  according  to  the  kind  of  current:  alternating  or  direct. 
With  the  latter  there  can  be  but  one  variation  in  the  conditions 
of  the  supply — the  line  pressure.  The  former  may  be  of  any 
commercial  potential,  frequency  or  phase;  for  railway  service 
a  comparatively  limited  number  of  potentials  and  frequen- 
cies have  been  standardized,  and  the  three-phase  and  single- 
phase  systems  are  used  exclusively  when  alternating  current  is 
employed. 

Classification  of  Electric  Motors. — Electric  motors  of  all 

42 


MOTORS  FOR  TRACTION  43 

types  may  be  classified  either  according  to  the  kind  of  circuit 
on  which  they  may  be  operated,  or  to  their  inherent  char- 
acteristics. In  the  former  classification,  the  natural  divisions 
are  alternating  current  and  direct  current.  The  most  im- 
portant types  of  motors  are  listed  below. 

I.  MOTORS  FOR  OPERATION  ON  ALTERNATING-CURRENT  CIRCUITS: 

Single-phase  Polyphase  (three-phase) 

Synchronous  Synchronous 

Asynchronous  Asynchronous  • 

Induction  Induction 

Squirrel-cage  Squirrel-cage 

Wound  secondary  Wound  secondary 

Commutator  Commutator 

Series  Various  types 

Plain 

Compensated 
Conductive 
Inductive 
Repulsion 

II.  MOTORS  FOR  OPERATION  ON  DIRECT-CURRENT  CIRCUITS: 

Series 
Shunt 
Compound 

Cumulative  winding 

Differential  winding. 

The  principal  characteristics  of  the  various  types  of  motors 
are  those  of  torque  and  speed.  Of  the  tw,o,  it  is  much  more 
useful  to  classify  them  as  regards  the  latter.  In  this  table  only 
two  speed  classifications  are  given:  constant  and  variable. 
Several  of  the  motors  may  have  performance  which  is  inter- 
mediate between  true  constant  speed  and  what  is  known  as 
"  variable  speed."  Such  types  have  either  been  omitted  or 
included  with  one  or  the  other  class. 

III.  CLASSIFICATION  AS  REGARDS  SPEED  CHARACTERISTICS: 

Constant  speed  Variable  speed 

Shunt  direct  current  Series  direct  current 

Synchronous  Series  alternating  current 

Induction  Repulsion 

Differential  Cumulative  compound 


44 


THE  ELECTRIC  RAILWAY 


Consider  first  the  two  principal  types  of  direct-current  motors, 
the  shunt-wound  and  the  series-wound  machines.  The  entire 
difference  between  them  lies  in  the  connections  of  the  field 
windings,  in  the  former  the  field  being  connected  in  series  with 
the  armature,  and  in  parallel  with  it  in  the  latter  type.  The 
shunt  motor,  having  its  field  excited  by  a  winding  connected 
to  the  supply  circuit  independent  of  the  armature,  has  a  field 
of  sensibly  constant  magnetic  strength ;  while  in  the  series  machine 
the  field  strength  is  directly  dependent  on  the  current  drawn 
through  the  armature. 

Torque  Characteristics. — In  any  electric  motor,  the  torque 
developed  by  the  armature  is  proportional  to  the  product  of  the 


1200 


1000 


D--  800 
ft: 


400 


200 


1200 


1000:5 
a 


800 


600 


400 


200 


50 


250 


100         150       200 
Current,  Amperes.    . 

FIG.  15.  —  Characteristic  curves  of  shunt  motor. 

field  flux,  the  number  and  arrangement  of  conductors  on  the 
armature,  and  the  current  through  them.  In  the  case  of  a  motor 
having  a  constant  field  strength,  the  torque  is  directly  pro- 
portional to  the  armature  current,  since  for  any  particular  design 
the  number  of  armature  conductors  is  fixed.  This  is  sub- 
stantially the  condition  which  exists  in  the  shunt  motor.  Al- 
though there  is  a  small  reduction  of  field  flux  with  increase  of 
armature  current,  the  field  strength  may  be  considered  sensibly 
constant,  hence  a  curve  drawn  between  armature  current  and 
torque  will  be  practically  a  straight  line,  as  shown  in  Fig.  15. 


MOTORS  FOR  TRACTION 


45 


Consider  a  motor  whose  field  current  is  proportional  to  its 
armature  current,  the  permeability  of  the  magnetic  circuit  re- 
maining constant.  The  field  flux  is  then  directly  proportional 
to  the  armature  current ;  and  the  torque,  depending  as  it  does  on 
the  product  of  the  field  flux  and  the  armature  current,  varies  as 
the  square  of  the  latter  (see  curved,  Fig.  16).  Such  a  relation 
would  exist  in  the  case  of  a  series  motor  with  an  unsaturated 
magnetic  circuit.  Practically,  it  is  not  attainable,  due  to 
variations  in  the  permeability  of  magnetic  materials  with  changes 
in  magnetizing  force. 


1400 


SO  100      .       150  200          250 

Current,  Amperes 

FIG.  16. — Characteristic  curves  of  series  motor. 

In  the  last  example,  if  the  area  of  the  magnetic  circuit  be  re- 
stricted, the  field  will  become  "saturated"  with  large  values  of 
current.  As  ordinarily  used,  the  term  " saturation"  does  not 
imply  that  there  is  no  gain  in  flux  with  increase  of  magnetizing 
current.  Even  though  the  magnetic  material  were  incapable  of 
carrying  any  further  induction  than  a  certain  maximum  value, 
the  flux  would  vary  with  the  magnetizing  current  at  the  same 
rate  as  it  would  with  a  magnetic  circuit  composed  wholly  of  air. 
This  condition  is  far  beyond  any  magnetic  densities  used  in 


46  THE  ELECTRIC  RAILWAY 

practice.  Since,  however,  the  change  in  flux  is  not  proportional 
to  the  variation  of  field  current,  the  torque  will  be  less  than  in  the 
case  of  the  unsaturated  motor.  The  torque-current  curve  will 
thus  lie  between  those  for  the  shunt  motor  and  the  unsaturated 
series  motor  (curve  J5,  Fig.  16). 

Speed  Characteristics. — The  counter  e.m.f.  of  a  direct-current 
motor  is  proportional  to  the  product  of  field  flux,  the  number  and 
arrangement  of  conductors  on  the  armature,  and  its  speed;  hence 


50         100         150        200         250 
Current,  Amperes. 

FIG.  17. — Comparison  of  series  and  shunt  motors. 

the  latter  varies  directly  with  the  counter  e.m.f.  and  inversely 
with  the  field  flux.  Since  the  fall  of  potential  due  to  resistance 
of  the  motor  windings  is  a  comparatively  small  amount,  the 
counter  e.m.f.  to  be  developed  is  nearly  constant,  and  it  follows 
that  the  speed  of  a  motor  with  a  constant  field  strength  varies 
but  little  with  the  armature  current.  This  is  practically  the  case 
of  the  shunt  motor,  the  drop  in  speed  from  no  load  to  full  load 
being  quite  small  in  a  well-designed  machine  (Fig.  15). 

In  a  motor  whose  field  strength  is  proportional  to  the  armature 
current,  such  as  the  hypothetical  "unsaturated"  series  motor,  the 


MOTORS  FOR  TRACTION  47 

speed  must  fall  in  inverse  proportion  to  the  armature  current,  for 
it  varies  inversely  with  the  field  flux.  The  speed  curve  of  such  a 
machine  is  an  equilateral  hyperbola,  as  shown  at  A' ,  Fig.  16.  For 
the  practical  series  motor,  with  saturated  field,  the  decrease  of 
speed  with  load  is  less  rapid  (Bf,  Fig.  16).  It  will,  however,  fall 
much  more  than  is  the  case  with  the  shunt  motor  of  equal 
rating. 

From  the  preceding  discussion  it  may  be  noted  that  for  values 
of  current  below  full  load  the  shunt  motor  -gives  more  torque 
per  ampere  than  the  series  motor,  while  above  this  point  the  con- 
ditions are  reversed.  Where  a  large  amount  of  torque  is  needed 
at  reduced  speeds,  as  in  the  case  of  starting  a  train,  the  series 
motor  gives  a  certain  tractive  effort  with  less  load  on  the  line 
than  the  shunt  motor.  If  the  shunt  motor  and  the  series  motor 
are  of  equal  capacity,  the  former  will  be  able  to  accelerate  the 
train  at  the  maximum  rate  practically  up  to  its  full  speed;  but 
this  is  considerably  lower  than  the  maximum  speed  of  the  cor- 
responding series  machine.  In  case  a  comparison  is  desired  on  the 
basis  of  motors  having  the  same  " balancing"  or  free-running 
speed,  they  will  be  as  shown  in  Fig.  17.  Here  the  series  motor  is 
the  same  as  in  the  preceding  comparison,  but  the  characteristics 
of  the  shunt  motor  are  changed,  by  gearing  or  otherwise,  to 
increase  the  speed  without  changing  the  horsepower  output. 
The  torque  is  correspondingly  lowered.  It  will  be  seen  at  once 
that  this  shunt  motor  cannot  possibly  give  the  same  accelerating 
torque  as  the  series  motor  without  imposing  an  excessive  overload 
on  the  former ;  and  the  torque  corresponding  to  a  given  value  of 
current  is  much  less  than  for  the  series  motor.  The  shunt  motor 
has  one  advantage,  in  that  it  can  accelerate  the  train  at  the 
maximum  rate  up  to  practically  full  speed.  This  partially,  but 
not  wholly,  compensates  for  the  lower  acceleration,  since  the 
series  motor  can  only  produce  its  maximum  torque  up  to  about 
half  speed.  This  advantage  is  slight,  as  may  be  seen  from 
Fig.  18,  which  shows  speed-time  curves  produced  by  the  applica- 
tion to  the  starting  of  a  particular  train  of  each  of  the  three 
motors  considered.  The  speed-time  curves  are  based  on  the  ap- 
plication of  a  maximum  value  of  one  and  one-half  times  full- 
load  current  during  the  acceleration  period.  The  series  motor 
gives  the  highest  acceleration,  but  this  falls  off  from  about  half 
speed  up  to  full  speed,  which  is  reached  only  after  a  long  time. 
The  shunt  motors,  on  the  other  hand,  give  maximum  accelera- 


48 


THE  ELECTRIC  RAILWAY 


tion  until  the  full  running  speed  is  reached,  after  which  the 
speed  is  constant. 

The  advantage  of  the  series  motor  is  greatest  where  the  run  is 
relatively  short.  In  many  railways,  especially  those  of  the  first 
and  second  classes  mentioned  in  Chapter  I,  the  motors  are  not 
allowed  to  accelerate  up  to  the  point  where  full  speed  is  attained, 
but  the  car  is  stopped  after  a  relatively  short  period  of  operation. 
With  long  runs,  the  time  spent  in  acceleration  is  comparatively 
unimportant,  and  a  lower  rate  is  permissible.  For  this  latter 
service  the  shunt  motor  would  have  the  advantage  of  operating 
at  practically  constant  speed  under  all  conditions  of  track.  The 


50       60       70       80       90       100      110       120       130 
Time, Seconds 


10       20      30       40 
FIG.  18. — Comparative  speed-time  curves  with  series  and  shunt  motors. 


advantages  of  the  series  type  of  motor  so  far  outweigh  those  of 
the  shunt,  that  up  to  the  present  time  the  latter  has  not  been 
seriously  considered  for  traction.  Its  counterpart  for  alternating- 
current  operation,  the  polyphase  induction  motor,  has  not  only 
received  favorable  attention,  but  is  actually  used  in  a  large 
number  of  equipments  operating  in  Europe.  This  success  is 
partly  due  to  the  fact  that  it  is  the  most  rugged  and  efficient  type 
of  alternating-current  motor  yet  designed. 

The  Direct-Current  Series  Motor. — The  direct-current  series 
motor  has  been  used  for  traction  ever  since  the  first  practical 
electric  roads  were  built.  Other  types  of  motor  have  been  used 
from  time  to  time,  but  none  has  the  excellent  operating  charac- 
teristics of  the  series  machine.  Since  about  97  per  cent,  of  all  the 


MOTORS  FOR  TRACTION 


49 


electric  railway  mileage  in  the  United  States  is  operated  with 
direct-current  series  motors,  a  careful  study  of  their  characteristics 
is  necessary. 

The  general  performance  of  this  type  of  motor  has  already  been 
discussed  briefly.  The  salient  characteristics  are  a  torque  which 
increases  with  the  load  at  a  rate  greater  than  the  first  power  of  the 
current,  and  a  speed  which  falls  off  rapidly  with  it,  especially  at 
the  smaller  loads.  These  curves  may  be  seen  in  Fig.  19,  which 
gives  the  performance  of  a  56  kw.  (1  hr.  rating)  railway  motor. 


4-000 


I 


100          150         ZOO        250 
Current,  Amperes. 

FIG.  19. — Curves  for  typical  series  railway  motor. 

Variation  of  Speed  Characteristic. — It  must  be  noted  that 
although  the  series  motor  is  usually  referred  to  as  a  "variable 
speed"  machine,  there  is  for  any  given  value  of  torque  a  cor- 
responding definite  speed  at  which  the  motor  will  operate;  so  that, 
if  the  tractive  effort  is  constant,  the  motor  will  run  at  one  fixed 
speed.  If  it  is  necessary  that  a  train  be  propelled  at  varying 
speeds  when  the  track  alignment  is  uniform,  some  means  must  be 
introduced  into  the  equipment  by  which  the  motor  speed  will  be 
altered  to  suit  the  conditions.  One  possible  method  of  doing  this 


50  THE  ELECTRIC  RAILWAY 

is  by  changing  the  gear  ratio.  This  means  is  actually  employed 
in  the  gasoline  automobile.  It  is  not,  however,  necessary  to  use 
such  a  method  with  the  series  motor,  since  a  variation  in  the 
e.m.f.  supplied  the  motor  will  cause  a  change  in  the  speed  for  a 
given  tractive  effort. 

The  speed  characteristic  may  be  readily  altered  by  varying  the 
potential  at  the  motor  terminals;  this  may  be  accomplished 
directly  by  changing  the  e.m.f.  supplied  the  motor,  or  by  placing 
resistance  in  series  with  it.  Details  of  methods  for  securing  these 
results  will  be  taken  up  in  Chapter  V. 

The  counter  e.m.f.  developed  by  a  direct-current  motor 
operating  on  a  constant  -potential  circuit  must  be  equal  to  the 
impressed  e.m.f.  less  the  IR  drop  in  the  windings.  Since  the 
resistance  of  a  well-designed  motor  is  quite  low,  the  IR  drop 
will  be  but  a  small  portion  of  the  impressed  potential  ;  it  is  rarely 
more  than  one-tenth  of  this  value  even  at  heavy  loads.  The 
counter  e.m.f.  must  therefore  be  nearly  constant.  Its  value 
depends  on  two  factors:  the  speed  of  the  armature,  and  the 
field  flux.  For  the  e.m.f.  developed  in  any  conductor  varies 
directly  as  the  flux  density,  the  speed,  the  length  of  the  con- 
ductor, and  its  arrangement  with  respect  to  the  field  and  the 
direction  of  motion.  Where  several  conductors  are  connected 
together,  the  e.m.f.  also  depends  on  the  number  of  them  and 
their  arrangement.  In  the  case  of  an  armature  these  factors  are 
fixed  for  a  particular  design,  and  may  be  included  in  a  general 
constant.  We  may  therefore  write: 


Ec  =  k$n  (1) 

where  Ec  is  the  counter  (or  direct)  e.m.f.  developed  by  an  arma- 
ture, k  is  a  constant  depending  on  the  design  of  the  winding,  <f> 
is  the  field  flux  cut  by  the  conductors  and  n  is  the  speed  of  revolu- 
tion. This  equation  may  also  be  written 

»  =  f;  a-) 

or,  in  other  words,  the  speed  of  a  motor  varies  directly  with 
the  counter  e.m.f.  and  inversely  with  the  field  flux. 

Since  the  counter  e.m.f.,  Ec,  may  be  represented  in  terms  of 
the  impressed  potential,  or 

Ec  =  E  -  Ir  (2) 


MOTORS  FOR  TRACTION 


51 


where  E  is  the  impressed  e.m.f.,  /  the  armature  current,  and  r 
the  resistance  through  which  that  current  has  to  pass,  equation 
(la)  may  be  rewritten 


50          100         150        200        250 
Current,  Amperes'. 

FIG.  20.  —  Speed  curves  for  series  motor  with  reduced  potentials. 

Consider  any  definite  value  of  current,  I\.  In  the  series  motor 
this  determines  both  the  IR  drop  and  the  field  flux,  3>.  For 
various  values  of  applied  e.m.f.,  EI,  Ez,  the  speed  may  be  found 
by  direct  proportion. 

El  -  I,r 


k 


-  J2r 


whence 


E,  - 


(4) 


(4a) 


This  latter  expression    (4a)    may   be   conveniently  used  for 
determining  the  speed  of  the  motor  when  any  potential  other 


52 


THE  ELECTRIC  RAILWAY 


than  normal  is  impressed  on  its  terminals.  The  curves  of 
speed  for  the  56  kw.  motor  shown  in  Fig.  19  are  redrawn  in  Fig. 
20  at  one-half  potential  (250  volts)  and  at  one-fourth  potential 
(125  volts).  It  may  be  seen  from  these  curves  that  the  speed 
is  slightly  less  than  half  its  normal  value  when  the  potential  is 
reduced  to  one-half,  and  somewhat  less  than  one-fourth  the 
normal  value  when  the  potential  is  reduced  to  one-fourth.  This 
is  because  the  IR  drop  is  a  larger  proportion  of  the  total,  the  lower 
the  impressed  e.m.f. 


50         100        150       200        250 
Amperes 

FIG.  21. — Speed  curve  for  series  motor  with  external  resistance. 

Variation  of  Speed  with  Resistance. — The  other  method  of 
changing  the  speed  by  variation  in  potential  is  by  the  insertion 
of  resistance  in  series  with  the  motor.  Its  action  may  be  deter- 
mined by  application  of  the  method  of  equation  (3),  as  shown  by 
the  following  relation: 


Ei-hr 

where  n\  is  the  normal  speed  at  current  /i,  n2  the  speed  with  an 
external  resistance  R  introduced  into  the  circuit,  and  the  other 
values  as  before.  In  Fig.  21  is  shown  the  speed  curve  for  the 
motor  of  Fig.  19  with  an  external  resistance  of  four  times  the  motor 


MOTORS  FOR  TRACTION  53 

resistance  added  in  series  with  it.  It  may  be  noted  that  the  effect 
of  this  added  resistance  is  quite  small  at  light  loads;  but  at 
heavy  loads  the  speed  is  reduced  until  the  motor  is  brought  to  a 
standstill.  In  order  to  obtain  the  same  speed  reduction  at  light 
loads  the  external  resistance  would  need  to  be  considerably 
greater. 

Torque  Characteristic.  —  It  is  also  necessary  to  determine 
the  effect  of  the  above  changes  on  the  torque  characteristic  of 
the  motor.  The  production  of  torque  depends  on  the  funda- 
mental principle  that  a  conductor  carrying  a  current  tends  to  be 
pushed  sidewise  out  of  any  magnetic  field  in  which  it  is  situated. 
The  value  of  this  push  varies  directly  with  the  current,  with 
the  flux  density,  and  with  the  length  of  the  armature  con- 
ductors and  their  number  and  arrangement.  For  any  par- 
ticular motor  they  are  permanently  arranged,  so  that  we  have 


D  =  k$I  (6) 

where  D  is  the  torque  produced  by  the  motor,  k  the  winding  con- 
stant, 3>  the  field  flux,  and  I  the  current  through  armature  and 
field.  It  may  be  seen  at  once  that  for  a  given  value  of  current, 
the  torque  of  the  series  motor  is  fixed,  since  the  armature  current 
also  determines  the  field  strength.  Changes  in  potential  have 
no  effect  on  the  torque  characteristic  of  the  series  motor,  and 
only  serve  to  vary  the  speed  at  which  any  torque  is  produced.1 

Variation  of  Field  Strength.  —  In  certain  cases  it  may  be  found 
desirable  to  vary  the  field  strength  of  the  series  motor.  Since 
the  field  and  armature  draw  their  current  through  the  same 
series  circuit,  it  is  necessary  to  divert  a  portion  of  it  from  the 
field  winding  or  to  actually  reduce  the  number  of  turns  on  the 
coils,  in  order  to  diminish  the  flux.  Either  of  these  methods 
may  be  used  in  practice,  as  is  explained  in  Chapter  V.  The 
two  methods  have  the  same  effect  on  the  characteristic 
performance. 

Referring  to  equation  (la),  it  may  be  seen  that  the  speed  of  a 
motor  varies  inversely  with  the  field  flux.  This  latter  depends 
on  the  field  current;  but  the  relation  is  not  a  direct  one.  The 
magnetic  circuit  is  made  up  of  a  number  of  materials  with 

1  A  small  change  in  losses  and  in  the  magnetic  relations  will  cause  a  slight 
difference  in  the  torque  produced  under  different  conditions,  but  these 
changes  are  so  small  as  to  have  little  effect  on  the  general  form  and  value 
of  the  torque  characteristic. 


54 


THE  ELECTRIC  RAILWAY 


different  magnetic  characteristics  and  widely  varying  area  of 
cross-section,  so  that  the  flux  densities  are  quite  different  in 
various  parts  of  the  circuit.  The  ability  of  a  material  to  carry 
flux  depends  on  its  permeability,  and  this  varies  widely  with 
different  values  of  magnetizing  force  and  with  the  physical  and 
chemical  composition  of  the  material.  To  determine  the  re- 
lation between  the  magnetizing  force  and  the  flux  produced  by 
it  would  necessitate  taking  the  saturation  curve  of  the  machine. 
In  the  series  motor,  however,  there  is  a  method  for  determining 
relative  values  of  flux  from  the  performance  curves.  Equation 


50 


£50 


100         150        200 
Current,  Amperes. 

FIG.  22. — Flux  curve  for  series  motor. 

The  torque  (or  approximately  the  tractive  effort)  per  ampere  is  a  direct  measure  of  the 
field  flux  in  the  series  motor. 

(6)  gives  the  relation  between  torque,  flux  and  current.  If 
the  torque  and  current  are  known  (as  for  example,  they  are 
given  in  the  curves  of  Fig.  19)  a  result  may  be  obtained  pro- 
portional to  the  values  of  flux: 

7=fc*  (7) 

A  curve  plotted  between  torque  per  ampere  and  amperes  (Fig. 
22)  will  then  represent  the  variation  in  flux  with  magnetizing 


MOTORS  FOR  TRACTION  55 

force.  This  relation  only  holds  true  in  the  case  of  motors  whose 
field  current  is  the  same  as  or  varies  directly  with  the  load 
current.  If  the  field  flux  of  a  motor  remain  constant,  as  in  the 
shunt  motor,  the  torque  varies  directly  with  the  load  current, 
according  to  equation  (6). 

To  determine  the  performance  of  a  motor  whose  field  strength 
has  been  changed  from  the  normal  value,  the  torque  should  be 
taken  corresponding  to  the  normal  field  strength,  and  its  varia- 
tion found  from  the  ratio  of  values  of  field  flux.  If  the  armature 
current  is  the  same  in  both  cases,  the  torque  will  be  in  direct 
proportion  to  the  flux.  That  is: 

D2       *2 

B;-*; 

where  DI  and  D2  are  values  of  torque  corresponding  to  normal 
field  flux  $1  and  changed  field  flux  3>2  respectively.  We  may 
then  write 

£>2  =  f^i  (8a) 

Since  only  the  relative  values  of  flux  are  needed,  they  may  be 
found  from  the  values  of  torque  per  ampere,  as  indicated  in 
equation  (7). 

The  effect  on  the  speed  of  weakening  the  field  may  be  seen 
from  equation  (3).  The  speed  will  vary  inversely  with  the  flux, 
so  that  for  a  decrease  in  flux  the  speed  will  be  correspondingly 
greater.  If  n\  be  the  speed  with  normal  field  flux,  and  n2  the 
speed  with  changed  field  flux,  then  we  have 

-  =  lr  0) 

ni       3>2 

where  n\  and  nz  are  the  values  of  speed  corresponding  to  normal 
field  flux  3>i  and  changed  field  flux  <£2  respectively.  From  this  we 
may  write 

$1 

w2  =  —  ni  (10) 

As  with  the  torque,  only  relative  values  of  the  flux,  which  may  be 
found  from  equation  (7),  are  needed  for  the  solution  of  the 
equation. 

The  effect  on  the  characteristic  curves  of  the  series  motor  of 
reducing  the  field  ampere  turns  to  one-half  the  normal  value  is 
shown  in  Fig.  23.  It  should  be  noted  that  although  the  magneto- 


56  THE  ELECTRIC  RAILWAY 

motive  force  has  been  reduced  to  one-half,  the  flux  is  not  lowered 
in  anything  like  the  same  proportion,  and  the  curves  are  not  so 
widely  different  as  might  be  anticipated. 

Reduction  of  field  ampere  turns  was  used  for  controlling  the 
performance  of  series  motors  in  the  early  days  of  electric  railways, 
but  was  abandoned  on  account  of  the  increased  tendency  to 
sparking  with  the  weak  field.  Modern  designs  of  railway 
motors,  using  interpole  construction,  have  made  possible  a  return 
to  the  early  method  of  control.  It  is  especially  advantageous  for 


4000 


500 


100        150         BOO        Z50 
Current,  Amperes. 

FIG.  23. — Characteristic  curves  of  series  motor  with  half  field. 

trains  which  have  to  operate  at  slow  schedule  speed  with  rapid 
acceleration  for  a  portion  of  the  run,  and  for  the  remainder 
operate  at  high  schedule  speed  with  few  stops. 

Losses  in  the  Series  Motor. — The  losses  which  occur  in  the 
series  motor,  while  of  the  same  character  as  for  any  electric 
machine,  differ  in  that  the  speed  and  the  flux  density  both  vary 
with  the  armature  current.  None  of  the  losses  are  constant, 
but  all  change  with  the  load.  They  may  be  classified  as 
follows : 


MOTORS  FOR  TRACTION  57 

Resistance  losses  (copper  losses) 

Armature  PR 

Field  PR 

Compensating  (interpole)  winding  PR 

Brush  loss 
Iron  losses 

Hysteresis 

Eddy  currents 
Mechanical  losses 

Bearing  friction 

Brush  friction 

Windage. 

Copper  loss,  being  the  product  of  the  current  squared  and  the 
resistance,  is  readily  found  for  the  series  motor.  The  windings 
being  all  in  series,  the  total  resistance  of  the  motor  may  be  taken 
and  the  entire  loss  calculated  at  once.  The  only  precaution  is  to 
remember  that  when  the  field  is  weakened  either  by  reducing  the 
number  of  turns,  or  by  shunting  the  winding,  the  resistance  is 
thereby  lessened. 

Brush  loss  is  a  function  of  the  current  through  the  brush  and 
the  drop  of  potential  in  it  and  in  the  contact  between  it  and  the 
commutator.  This  drop  is  largely  independent  of  the  current, 
being  a  definite  amount  at  no  load  and  increasing  at  a  lower  rate 
than  in  proportion  thereto.  The  loss  may  be  determined  with 
various  degrees  of  accuracy  by  the  application  of  empirical  for- 
mulae to  be  found  in  electrical  handbooks. 

Iron  loss  consists  of  two  distinct  components :  hysteresis  loss  and 
eddy  currents.  The  former  varies  approximately  as  the  1.6 
power  of  the  flux  density,  and  directly  as  the  frequency;  the 
latter  as  the  square  of  the  flux  density  and  as  the  square  of  the 
speed.  Since  the  speed  decreases  as  the  current  and  flux  in- 
crease, the  variation  of  iron  Loss  with  load  is  quite  involved.  It 
is  usually  determined  for  different  current  values  at  various 
potentials,  as  shown  in  Fig.  24.  Ordinarily  the  determination  of 
iron  loss  is  made  experimentally,  and  it  is  not  readily  possible  to 
formulate  an  equation  expressing  the  theoretical  conditions  of  its 
variation. 

The  mechanical  losses  depend  only  on  the  speed  of  the  machine. 
Brush  friction  varies  directly  as  the  speed,  and  bearing  friction 
and  windage  as  a  power  of  the  speed  between  the  first  and 
second.  Their  separation  is  difficult,  and  is  not  ordinarily 


58 


THE  ELECTRIC  RAILWAY 


attempted.  The  total  value  of  these  losses  is  quite  small  unless 
the  armature  is  specially  constructed  to  circulate  air  through 
the  windings  for  cooling. 

Efficiency  of  the  Series  Motor. — In  any  machine,  the  effi- 
ciency is  the  ratio  of  output  to  input.  It  may  also  be  stated 
as  the  ratio  of  output  to  output  plus  losses,  or  the  ratio  of  in- 
put minus  losses  to  input.  Hence  if  any  two  of  the  quantities 


400 


100 


500 


200        300       400 

E.M.F.,  Volts. 
FIG.  24. — Iron  loss  curves  for  series  motor. 

output,  input,  losses  or  efficiency  be  given,  the  other  two  may 
be  found  by  a  simple  calculation. 

The  efficiency  of  the  series  motor  may  be  determined  by  any 
of  the  methods  outlined  in  the  last  paragraph.  In  testing 
series  motors,  it  is  difficult  and  somewhat  unsatisfactory  to  load 
them  with  a  prony  brake,  as  is  necessary  to  determine  efficiency 
by  the  input-output  method.  Ordinarily  the  separate  losses 
are  obtained,  and  the  performance  found  therefrom.  For 
methods  of  calculating  efficiency  from  losses,  reference  may  be 
made  to  any  text-book  on  electrical  testing. 

Alternating-Current  Commutator  Motors. — For  many  years 
attempts  were  made  to  produce  motors  which  would  operate 


MOTORS  FOR  TRACTION  59 

satisfactorily  on  single-phase  circuits,  and  have  characteristics 
suitable  for  railway  purposes.  When  the  alternating-current 
system  of  transmission  was  first  brought  out,  motors  were 
designed  which  were  practically  the  same  as  the  direct-current 
series  motor.  None  of  them  was  successful,  since  an  incorrect 
understanding  of  the  nature  of  iron  loss  led  to  the  use  of  a  solid 
iron  structure  for  carrying  the  alternating  magnetic  flux.  In 
1902  a  new  type  of  single-phase  motor  was  announced,  which 
was  the  exact  counterpart  of  the  direct-current  series  motor, 
modified  for  use  on  alternating  current  by  having  a  number  of 
special  features.  In  order  to  understand  the  operation  of  this 
type  of  motor,  it  will  be  well  to  trace  its  development  from  the 
direct-current  machine. 

Consider  a  motor  operating  on  direct  current,  the  field  and 
armature  being  in  series.  If,  for  any  reason,  the  current  through 
the  motor  is  reversed,  there  will  be  no  permanent  result  what- 
ever on  the  operation.  This  can  be  repeated  as  often  as  desired, 
provided  it  is  not  done  more  than  a  few  times  a  minute.  In 
case  an  attempt  is  made  to  reverse  the  motor  too  frequently, 
several  effects  are  to  be  observed:  (1)  the  amount  of  current 
that  can  be  forced  through  its  circuits  will  be  reduced,  owing 
to  the  inductance  of  the  field  windings;  (2)  due  to  this  inductance, 
the  current  will  lag  behind  the  electromotive  force;  (3)  the  iron 
in  the  magnetic  circuit  will  heat  up  on  account  of  the  hysteresis 
and  eddy  currents  caused  by  the  variable  flux;  (4)  there  will  be 
severe  sparking  at  the  commutator. 

It  is  possible  to  reduce  the  iron  loss  to  a  reasonable  amount 
by  using  a  good  grade  of  electrical  steel  and  by  lamination  of 
the  metal.  This  is  one  of  the  first  requirements  of  any  good 
alternating-current  motor.  The  inductance  of  the  field  can  be 
lessened  by  cutting  down  the  number  of  field  turns.  A  con- 
siderable reduction  may  be  made  in  the  field  ampere  turns 
without  a  great  diminution  in  the  flux,  since  in  modern  direct- 
current  motors  the  iron  is  worked  at  a  high  degree  of  saturation 
(see  Fig.  22).  This  will  reduce  the  inductance  of  the  field  wind- 
ing, and  hence  diminish  the  lag  of  the  motor  current.  The 
power  factor  can  be  still  further  improved  by  the  insertion  in  the 
circuit  of  compensating  coils,  of  the  general  nature  of  an  inter- 
pole  winding,  with  a  number  of  ampere  turns  sufficient  to  neu- 
tralize the  magnetomotive  force  of  the  armature.  This  will 
both  tend  to  lessen  the  reactance  and  to  improve  commutation. 


60 


THE  ELECTRIC  RAILWAY 


The  use  of  these  devices  will  in  some  cases  produce  a  motor 
which  may  operate  on  frequencies  up  to  about  25  cycles.  In 
general,  however,  additional  means  must  be  taken  to  reduce 
the  sparking  to  a  point  where  it  is  not  objectionable. 

Reference  to  Fig.  25  will  show  the  reasons  for  the  excessive 
sparking  of  the  single-phase  motor.  Consider  an  armature  ro- 
tating in  the  field  produced  by  current  drawn  from  the  line  through 
the  field  winding.  Whether  the  flux  be  constant  or  not,  there 
will  be  an  e.m.f.  developed  in  the  armature,  its  maximum  value 
per  turn  being  induced  in  the  conductors  directly  under  the  poles. 

The  maximum  total  appears 
at  the  brushes  B}  B.  If  the 
flux  be  varying  in  value  (i.e., 
alternating)  there  will  be  an 
e.m.f.  produced  due  to  the 
change  in  flux,  which  will 
have  its  maximum  per  turn 
in  the  conductors  between 
the  poles,  and  its  total  maxi- 
mum at  the  brushes  A,  A. 
It  may  be  seen  that  these 
two  e.m.f.'s  are  entirely  inde- 
pendent, the  former,  which 
we  may  call  the  "  speed 
e.m.f.,"  depending  on  the 
mechanical  rate  of  cutting  the 
flux  with  the  armature  con- 
ductors, due  to  the  speed  of 

FIG.  25.-Single-phase  series  motor,     rotation;     while     the     latter, 

which    may   be    termed    the 

" transformer  e.m.f.,"  depends  on  the  rate  of  change  of  the  field 
flux  caused  by  the  cyclic  variation  in  the  magnetizing  current. 
To  operate  as  a  normal  series  motor,  the  speed  e.m.f.  is  the  one 
which  must  be  commutated,  and  the  transformer  e.m.f.  must 
be  entirely  disregarded.  The  brushes  should  therefore  be 
placed  in  the  positions  B,  B.  It  is  evident  that  the  turns  which 
are  short-circuited  by  the  brushes  are  the  very  ones  which  are 
generating  the  maximum  e.m.f.  due  to  transformer  action, 
and  there  is  a  tendency  toward  severe  sparking,  even  when  the 
distortion  of  the  field  due  to  the  cross  ampere  turns  of  the 
armature  has  been  entirely  removed  by  a  suitable  interpole  or 


MOTORS  FOR  TRACTION  61 

compensating  winding.  Reducing  the  number  of  armature 
turns  per  commutator  bar  will  dimmish  the  current  in  the 
short-circuit,  but  not  as  a  rule  to  a  satisfactory  value.  An 
additional  method  which  has  been  employed  by  one  of  the  large 
manufacturers  in  this  country  is  to  introduce  between  each 
commutator  bar  and  the  armature  winding,  a  fixed  resistance 
of  proper  amount,  sufficient  to  limit  the  current  in  the  short- 
circuited  coil  to  a  safe  value.  The  action  of  such  resistance  may 
be  seen  in  Fig.  26.  It  will  be  noticed  that  only  those  resistance 
leads  which  connect  to  the  coils  undergoing  commutation  are 
in  circuit,  and  that  the  ones  carrying  current  are  in  parallel 
with  each  other,  so  that  if  the  brush  covers  several  bars,  the 
resistance  inserted  in  the  path  of  the  main  current  can  be  in- 


Brush 


Commutator 


Res.  Leads 


Arm.  Winding 


FIG.  26. — Use  of  resistance  leads  in  single-phase  motor. 

considerable,  and  yet  the  resistance  in  the  local  short-circuit  may 
be  sufficient  to  reduce  the  sparking  materially.  The  proper 
proportioning  of  these  resistance  leads  is  a  question  of  con- 
siderable importance  in  making  a  successful  single-phase  motor 
of  the  series  type. 

Frequencies  for  Single-Phase  Motors. — The  general  theory  of 
the  single-phase  series  motor,  as  developed  above,  would  indi- 
cate that  its  performance  will  be  better  the  lower  the  frequency. 
This  leads  to  the  logical  conclusion  that  the  best  number  of 
cycles  is  zero,  or  in  other  words,  that  the  perfomance  of  the 
machine  is  best  on  direct  current.  While  this  is  not  strictly 
true,  it  does  apply  to  a  certain  extent;  and  it  is  possible  to  operate 
the  same  motor  both  on  alternating-  and  direct-current  circuits. 
The  highest  frequency  which  can  be  used  for  a  particular  machine 
depends  on  the  reactance  of  the  windings,  the  iron  losses,  and 
the  commutation.  All  these  quantities  vary  as  functions  of 


62  THE  ELECTRIC  RAILWAY 

the  number  of  cycles.  Commercial  designs  of  single-phase 
series  motors  have  been  made  to  operate  on  circuits  up  to  25 
cycles  per  second;  but  the  limitations  make  it  exceedingly  difficult 
to  produce  motors  of  this  type  for  higher  frequencies.  When 
designed  for  operation  on  a  25-cycle  circuit,  the  series  motor 
will  weigh  from  10  per  cent,  to  25  per  cent,  more  than  a  machine 
of  equal  rating  for  direct  current. 

The  auxiliary  equipment,  such  as  transformers  and  regulators, 
shows  an  increase  of  capacity  at  the  higher  frequencies.  This 
tends  to  offset  the  gains  made  in  the  motor  performance  when 
the  number  of  cycles  is  reduced.  Manufacturers  of  single- 
phase  equipment  consider  that  the  best  compromise  is  the  use 
of  15  to  17  cycles,  which  gives  a  marked  increase  in  motor 
capacity  over  that  at  25  cycles,  while  at  the  same  time  the 
auxiliary  equipment  is  not  excessively  heavy.  The  electrical 
performance  of  the  series  motor  at  this  lower  frequency  is 
considerably  improved. 

While  the  reduction  in  frequency  is  entirely  beneficial  to 
the  series  motor,  the  effect  on  the  repulsion  motor  is  not  so  good. 
As  is  shown  in  the  following  paragraphs,  motors  of  the  repulsion 
type  have  some  of  the  characteristics  of  the  transformer,  and  a 
reduction  in  frequency  therefore  tends  to. increase  the  weight 
somewhat.  The  commutation  is  also  better  at  high  frequencies, 
since  the  speed  e.m.f.  is  disregarded  to  a  considerable  extent 
and  the  transformer  e.m.f.  commutated.  The  general  char- 
acteristics of  the  repulsion  motor  are  not,  however,  so  good  for 
traction  as  those  of  the  series  type. 

Variations  of  the  Alternating-Current  Series  Motor. — Due  to 
the  inductive  effects  of  alternating  currents,  the  arrangement  of 
circuits  in  the  single-phase  motor  is  open  to  considerable  varia- 
tion without  interfering  with  the .  performance  to  any  marked 
extent.  Leaving  out  of  consideration  the  plain  series  motor, 
consisting  of  only  an  armature  and  a  set  of  field  coils,  and  which 
is  not  an  operative  success,  we  can  have  three  different  types 
of  series  motor. 

Fig.  27  shows  the  ordinary  type  of  series  motor,  described 
above,  which  is  commonly  known  as  the  "  conductively  com- 
pensated" type.  In  this,  as  in  the  direct-current  series  motor 
with  interpoles,  all  the  windings  are  in  series. 

Since  the  armature  winding  is  a  source  of  magnetic  flux,  the 
current  for  the  compensating  coils  may  be  obtained  by  trans- 


MOTORS  FOR  TRACTION 


63 


former  action  from  this  flux,  without  connection  to  the  main 
circuit.  Such  a  motor,  known  as  the  "  inductively  compen- 
sated" type,  is  shown  diagrammatically  in  Fig.  28. 


Compensating 
Winding 


UUUU 

Field 


FIG.  27.— Conductively  compensated 
single-phase  series  motor. 

In  this  machine  the  armature,  compensating 
winding  and  field  are  all  in  series.  It  will 
operate  either  on  alternating  or  on  direct  current. 


Compensating 
Winding 


JLQJU 

Field. 


FIG.  28. — Inductively  compen- 
sated single-phase  series  motor. 

In  this  machine  the  compensating 
winding  is  short-circuited,  the  current 
in  it  being  produced  by  induction 
from  the  armature. 


It  is  possible  to  go  a  step  further,  and  let  the  armature  flux 
excite  both  the  compensating  coil  and  the  main  field,  as  shown  in 
Fig.  29,  which  illustrates  the  " induction  series"  motor.  Of  the 
three  types,  the  former  two  are  used  in  practice,  the  conductively 


FIG.  29. — Induction  series  motor. 


In  this  machine  both  the  field  and  the  com- 
pensating winding  are  short-circuited,  the  cur- 
rent in  them  being  induced  from  the  arma- 
ture, which  is  connected  to  the  line. 


FIG.  30. — Atkinson  repulsion 
motor. 

This  machine  is  electrically  the  re- 
verse of  the  induction  series  motor, 
the  armature  being  short-circuited  and 
the  other  windings  connected  to  the 
line. 


compensated  motor  finding  its  use  principally  where  it  is  neces- 
sary to  operate  the  same  machine  on  both  alternating  and  direct 
current. 


64  THE  ELECTRIC  RAILWAY 

Repulsion  Motor. — As  it  is  possible  to  make  either  coil  of  a 
transformer  the  primary,  so  the  connections  of  the  induction 
series  motor  may  be  reversed  to  make  the  field  and  compensating 
windings  the  primary,  and  the  armature  the  secondary,  circuit. 
In  this  form,  shown  in  Fig.  30,  the  machine  is  known  as  the 
Atkinson  repulsion  motor.  It  may  also  be  considered  as  a 
development  of  the  plain  repulsion  motor,  which  is  shown  in  Fig. 
31.  In  the  latter  type  use  is  made  of  the  transformer  e.m.f., 
which  is  entirely  disregarded  in  the  series  motor.  The  brushes 
are  placed  at  an  angle  with  the  field,  so  as  to  utilize  portions  of 
both  the  transformer  e.m.f.  and  of  the  speed  e.m.f.  in  order  to 
obtain  variable  speed  characteristics.  The 
repulsion  motor  has  a  great  advantage 
over  the  series  motor,  in  that  the  primary, 
being  the  stationary  member,  can  be  con- 
nected to  the  supply  circuit  without  mov- 
able contacts,  as  when  the  current  must 
be  led  through  a  commutator;  the  primary 
can  therefore  be  wound  for  relatively 
high  potentials.  It  is  also  possible,  since 
the  coils  generating  the  maximum  trans- 
former e.m.f.  are  not  short-circuited,  to 
FIG.  31. — Plain  repulsion  operate  it  on  somewhat  higher  frequencies 
m°tor.  than  with  the  series  motor.  At  starting 

This  differs  from  the  motor      .  .  .  ,     .      ,  , 

shown  in  Fig.  30  in  that  the  the  short-circuit  current  is  lower  than  in 

compensating  and  the  exciting      ,  .  1,1  • ,  <• 

windings  are  combined.    For  the  series    motor,    and    the    necessity   of 

that    reason  the   brushes   are          .  .    .  ,        ,  ,     ,  . , 

placed  at  an  angle  with  the  using  resistance  leads  much  less,  so  that 
by  careful  design  they  may  be  omitted. 

But  in  general  the  characteristics  of  the  repulsion  motor  are  not 
so  well  suited  for  railway  work  as  are  those  of  the  series  motor, 
and  it  never  has  become  popular  for  this  class  of  service. 

Compensated  Repulsion  Motor. — A  modification  of  the 
repulsion  motor,  known  as  the  compensated  repulsion  motor,  or 
the  Latour-Winter-Eichberg  motor,  has  been  developed  to 
obtain  the  advantages  of  both  the  series  and  the  repulsion  types. 
This  motor  (Fig.  32),  has  two  separate  sets  of  brushes,  one  set 
short-circuited,  the  other  connected  in  series  with  the  field.  In 
this  way  it  combines  the  characteristics  of  both  the  series  and  the 
repulsion  types.  It  has  been  used  to  some  extent  in  electrifica- 
tion work  in  Europe,  but  has  not  been  applied  in  the  United 
States. 


MOTORS  FOR  TRACTION 


65 


Performance    of    the    Alternating-Current    Series    Motor. — 

Referring  to  the  vector  diagram  of  the  e.m.f.'s  in  the  series 
motor,  Fig.  33,  it  may  be  seen  that  the  total  potential  at  the 
motor  terminals  is  divided  into  three  components:  the  drop  OB 
across  the  field,  the  drop  BD  across  the  armature,  and  the  speed 
e.m.f.  DE.  For  any  given  current  value,  the  two  drops  are  constant, 
no  matter  what  the  speed.1  If  the  motor 
is  at  a  standstill,  these  drops  will  consti- 
tute the  entire  potential  OD  at  the  motor 
terminals.  As  the  speed  of  the  motor  is 
increased  to  give  a  counter  e.m.f.  DE}  it 
must  be  accompanied  by  an  increase  in 
the  terminal  potential,  as  given  by  the 
vector  OE.  Since  the  speed  e.m.f.  must 
be  in  phase  with  the  current,  while  the 
armature  and  field  drops  are  always  ahead 

of  it,  it  may  be  seen  that  an  increase  of   ^ 

j       .„    :  FIG.  32.— Compensated 

speed   will   improve   the  power  factor  of         repulsion  motor. 

the  motor.     By  keeping  the  reactances  in 

the  circuit  down  to  reasonable  values,  the 

normal  operating  power  factor  of  the  motor 

may  be  made  very  satisfactory;  that  is,  it  can  be  made  as  good 

as  or  better  than  the  power  factor  of  induction  motors  of  similar 

capacity. 


chJrac\eScsne0f 


FIG.  33. — E.  m.  f.  and  current  relations  in  single-phase  series  motor. 

The  characteristics  of  a  typical  single-phase  series  motor  are 
shown  in  Fig.  34.  The  speed  curve  is  more  dropping  than  with 
the  direct-current  series  motor,  due  to  the  lower  saturation  of  the 
magnetic  circuit.  For  the  same  reason  the  tractive  effort 

1  The  armature  and  field  drops  are  each  equal  to  the  product  of  the 
current  by  the  impedance  of  the  circuit.     Since  the  frequency  is  constant, 
the  reactances  are  practically  constant  in  any  particular  machine.     They 
will  be  changed  slightly  by  variations  in  iron  loss  at  different  speeds. 
5 


66 


THE  ELECTRIC  RAILWAY 


approximates  more  nearly  the  parabolic  form  than  in  the  com- 
mercial direct-current  series  motor.  The  power  factor  approaches 
unity  at  zero  current,  and  decreases  from  this  value  almost  uni- 
formly in  proportion  to  the  load. 


120      60 


200       400         600        800 
Current,  Amperes. 


1000 


FIG.  34. — Characteristics  of  single-phase  series  motor. 

Note  that  the  speed  curve  is  more  dropping  than  for  the  normal  direct-current  series 
motor,  on  account  of  the  lower  saturation  in  the  magnetic  field. 

Variation  of  Single-Phase  Motor  Characteristics. — The  charac- 
teristics of  the  alternating-current  series  motor  may  be  varied 
in  much  the  same  manner  as  with  the  direct-current  series  motor. 
The  three  methods  which  may  be  used  are: 

1.  Variation  of  terminal  potential. 

2.  Insertion  of  series  resistance. 

3.  Variation  of  field  strength  independently  of 
armature  strength. 

The  first  method  is  more  readily  applicable  than  with  the  direct- 
current  motor,  since  alternating  e.m.f.'s  of  any  desired  value  may 
be  secured  with  the  aid  of  a  stationary  transformer.  The  ease  in 
obtaining  change  of  motor  potential  makes  the  other  methods  of 
control  unnecessary.  The  use  of  series  resistance  is  uneco- 
nomical, and  persists  with  direct-current  motors  only  as  a  matter 
of  necessity.  The  variation  of  field  flux  in  the  alternating- 


MOTORS  FOR  TRACTION  67 

current  motor  is  undesirable,  since  to  make  a  good  commercial 
machine  the  flux  has  to  be  cut  down  normally  to  a  minimum,  and 
further  reduction  is  unwise. 

When  the  terminal  e.m.f.  is  lowered,  it  is  evident  that  the 
power  factor  will  be  reduced,  since  the  quadrature  component 
of  potential  remains  about  constant,  while  that  in  phase  is 
diminished,  due  to  the  lessened  speed.  As  with  the  direct- 
current  series  motor,  a  reduction  in  potential  does  not  change  the 
torque  to  any  great  degree.  Since  the  potential  in  an  alternating- 
current  circuit  may  be  varied  at  will  either  by  means  of  a  station- 
ary transformer  with  a  number  of  taps  on  the  secondary,  or  by 
a  transformer  with  a  rotatable  secondary  (induction  regulator), 
it  is  easy  to  obtain  a  wide  variation  in  potential  without  the  need 
for  re-connecting  the  motors,  as  in  a  series-parallel  combination, 
and  without  the  loss  inherent  to  the  use  of  resistance  in  the 
armature  circuit. 

Commutation  in  Single-Phase  Motors. — A  comparison  of  the 
circuits  of  the  series  and  the  repulsion  motors  makes  it  evident 
that  the  series  motor  has  its  brushes  placed  in  such  a  position 
that  the  transformer  e.m.f.  is  short-circuited  at  starting;  while 
the  repulsion  motor  short-circuits  the  speed  e.m.f.  The  re- 
pulsion motor  should  therefore  have  better  commutation  when 
starting,  while  the  performance  of  the  series  motor  in  this  respect 
will  be  superior  at  speeds  above  synchronism.  At  synchronous 
speed  the  e.m.f.  developed  by  transformer  action  is  equal  to  that 
produced  by  the  conductors  of  the  armature  cutting  the  field 
flux,  so  that  the  potential  is  uniform  at  all  points  around  the 
commutator.  At  this  speed  the  sparking  will  be  the  same  no 
matter  where  the  brushes  are  placed.  The  various  methods  used 
for  improving  the  commutation  make  the  series  motor  satis- 
factory at  starting;  but  so  far  the  repulsion  motor  has  not  given 
good  results  as  regards  sparking  at  speeds  much  above  synchro- 
nism. Since  the  power  factor  of  the  series  motor  is  better  as  the 
speed  increases,  it  has  a  considerable  advantage  in  performance 
for  high-speed  work. 

The  Polyphase  Induction  Motor. — The  polyphase  induction 
motor  is  so  well  known,  and  its  characteristics  have  been  so  fully 
described,  that  no  general  treatment  will  be  entered  into  here. 
It  is  sufficient  to  understand  that  the  motor  possesses  performance 
characteristics  similar  to  those  of  the  shunt  motor,  as  shown  in 
Fig.  35.  If  the  machine  is  well  designed,  the  drop  in  speed  from 


68 


THE  ELECTRIC  RAILWAY 


no  load  to  full  load  is  but  a  small  amount,  rarely  over  5  per  cent. 
The  normal  speed-torque  curve  of  such  a  motor  is  given  a 
" Notch  7."  It  will  be  noticed  that  the  effort  available  at  start- 
ing is  considerably  less  than  the  maximum  running  torque.  It 
may  further  be  shown  that  to  produce  this  starting  torque 
requires  a  relatively  large  current,  and  at  a  low  power  factor. 
If  the  secondary  resistance  of  the  motor  be  greater,  a  curve 
such  as  "  Notch  6"  may  be  obtained.  Here  the  starting  torque 
is  increased;  but  in  order  to  accomplish  this  result,  the  efficiency 
over  the  entire  working  range  has  to  be  sacrificed.  By  con- 
siderably increasing  the  secondary  resistance,  as  by  the  use  of 


250  500  750  1000 

Torque,   Pounds  at  One  Foot  Radius. 
FIG.  35. — Characteristics  of  polyphase  induction  motor. 

external  resistors,  the  starting  torque  may  be  increased  to  the 
maximum  possible  value,  as  at  "  Notch  5;"  or,  if  it  be  desired 
to  reduce  the  starting  current  further,  and  the  maximum  torque 
is  not  needed  at  starting,  additional  resistance  will  give  curves 
such  as  Notches  1,  2,  etc.  In  all  of  these  cases,  however,  the 
efficiency  is  very  much  reduced,  being  in  no  case  as  great  as  the 
speed  in  per  cent,  of  synchronism.  It  is  evident,  then,  that  to 
get  efficient  operation,  the  resistance  must  be  inserted  only 
during  the  starting  period,  it  being  gradually  cut  out  of  the 
circuit  as  the  speed  increases,  until  the  motor  is  operating  with 
short-circuited  secondary.  With  this  connection  the  motor  will 
operate  at  practically  constant  speed. 


MOTORS  FOR  TRACTION  69 

Another  method  of  reducing  the  speed  at  starting  is  to  lower 
the  potential  applied  to  the  terminals.  Since  the  motor  receives 
its  magnetizing  current  and  the  working  current  in  the  same 
winding,  any  reduction  of  the  potential  will  decrease  the  field 
strength  as  well  as  the  load  current.  In  normal  induction  motors, 
the  field  iron  is  practically  unsaturated,  so  that  the  flux  is  lessened 
nearly  in  proportion  to  the  reduction  of  potential.  The  decrease 
in  primary  potential  causes  a  similar  reduction  in  the  secondary 
induced  e.m.f.,  so  that  the  secondary  current  is  lessened.  It 
follows  that  the  torque  produced  at  any  given  value  of  load 
current  varies  as  the  square  of  the  applied  potential.  When  the 
primary  potential  is  reduced  the  power  factor  and  the  efficiency 
are  also  lowered,  so  that  the  performance  is  poor.  A  further 
effect,  due  to  the  larger  proportion  of  losses  in  the  motor,  is  that 
the  heating  at  any  given  primary  current  is  increased  and  the 
capacity  of  the  motor  reduced.  If  the  induction  motor  is  used 
for  starting  heavy  trains,  this  method  of  speed  control  is  not  to  be 
recommended;  and  in  any  case  it  is  far  inferior  to  the  first  method, 
by  insertion  of  resistance  in  the  secondary  circuit. 

The  induction  motor  inherently  must  operate  at  a  speed 
somewhat  below  synchronism;  and  we  have  seen  that  the  normal 
curve  does  not  fall  far  below  this  value.  It  is  possible  to  change 
the  speed  of  the  motor  if  the  synchronous  speed  can  be  changed ; 
and  this  can  be  done  without  any  great  sacrifice  of  power  factor 
or  efficiency.  There  are  two  methods  by  which  the  synchronous 
speed  may  be  altered:  by  variation  of  the  frequency,  and  by  a 
change  in  the  number  of  poles  on  the  primary  and  secondary.  No 
variation  in  frequency  can  be  expected  in  the  supply  circuit,  so 
any  change  made  must  be  in  the  control  of  the  motor.  This  is 
usually  done  by  " cascade  control"  or  " concatenation,"  in 
which  the  secondary  current  from  one  induction  motor  is  fed 
into  the  primary  of  another  motor,  the  two  being  mechanically 
connected  together  so  that  they  must  run  at  the  same  speed. 
This  will  be  described  more  in  detail  in  connection  with  methods 
of  control. 

The  number  of  poles  on  an  induction  motor  may  be  changed 
much  more  readily  than  on  a  direct-current  motor,  since  the  field 
is  usually  constructed  with  a  distributed  winding.  The  inclusion 
of  more  or  less  coils  in  a  group  makes  it  possible  to  re-connect  the 
winding  to  give  two  or  more  sets  of  poles  with  the  same  field 
coils.  To  get  more  than  two  sets  of  poles  with  the  same  coils 


70  THE  ELECTRIC  RAILWAY 

complicates  the  winding  to  an  extent  where  it  is  not  practical; 
so  for  such  cases  the  primary  and  secondary  parts  of  the  motor 
are  each  supplied  with  two  or  more  separate  windings,  in  case 
more  than  two  speeds  in  the  ratio  of  2  : 1  are  desired.  This 
method  of  speed  control  has  been  worked  satisfactorily  in  a  con- 
siderable number  of  European  locomotives;  but  is  too  cumber- 
some for  use  with  individual  motor  cars,  especially  where  train 
operation  is  desirable  on  the  multiple-unit  system. 

Induction  Motor  Performance. — Under  normal  conditions, 
the  efficiency  of  the  induction  motor  can  be  made  at  least  as  high 
as  that  of  the  best  direct-current  series  motors,  and  with  a  some- 
what smaller  weight  per  unit  of  output.  The  efficiency  is  some- 
what better  than  that  of  the  single-phase  series  motor,  being  about 
equal  to  the  efficiency  of  the  direct-current  series  motor.  The 
power  factor  is  at  least  as  low  as,  or  often  lower  than,  that  of  the 
single-phase  motors,  so  that  the  line  current  required  is  equal  to 
or  somewhat  greater  than  that  required  for  the  series  motor. 
Further  than  this,  it  must  be  remembered  that  the  induction 
motor  operates  only  on  a  polyphase  circuit,  so  that  at  least  two 
trolley  wires  are  necessary,  using  the  track  for  the  third  con- 
ductor. If  it  is  possible  to  install  a  rotating  phase  changer  on 
the  locomotive,  polyphase  motors  may  be  used  on  a  single-phase 
supply  system.  This  is  actually  being  done  on  one  American 
railroad  at  the  present  time. 


CHAPTER  IV 
RAILWAY  MOTOR  CONSTRUCTION 

Motor  Development. — Although  the  first  experimental  electric 
railway  was  built  in  1835,  and  various  inventors  were  from  time 
to  time  developing  model  electric  locomotives,  it  was  not  until 
the  year  1879  that  anything  resembling  a  practical  electric 
road  was  produced.  From  that  time  the  improvement  was 
rapid,  and  it  was  only  a  comparatively  few  years  until  the 
essentials  of  the  modern  electric  railway  had  been  invented  and 
applied. 

The  motors  used  during  the  first  or  experimental  period, 
from  1835  to  1879,  were  mere  toys,  and  had  no  practical  operating 
value.  In  the  latter  year,  the  great  engineering  firm  of  Siemens 
and  Halske  exhibited  an  electric  locomotive  designed  to  draw  a 
light  train  of  passenger  cars.  This  train  was  displayed  at  the 
Berlin  exposition.  It  marked  the  change  from  a  scientific'  toy 
to  a  practical  means  of  train  propulsion.  The  Siemens  loco- 
motive was  equipped  with  a  single  stationary  type  motor, 
mounted  on  the  platform,  and  belted  to  the  axle. 

In  the  next  few  years  a  large  number  of  inventors,  both  in 
America  and  in  Europe,  produced  electric  locomotives  and 
motor  cars  which  were  more  or  less  successful.  In  all  of  the 
earlier  types  the  motors  were  the  ordinary  stationary  machines, 
usually  applied  to  the  work  without  any  change  whatever.  In 
some  cases  even  arc-light  generators  were  used  as  motors.  It 
must  be  understood  that  the  equipment  in  these  early  roads  was 
exceedingly  crude.  This  was  not  surprising,  since  the  applica- 
tion of  electrical  machinery  in  general  had  just  begun,  and 
practically  none  of  the  present  theory  had  been  developed. 

Early  Motors. — In  the  early  electric  railways  in  this  country 
the  practice  mentioned  in  the  first  road  (that  of  the  Siemens 
and  Halske  firm)  of  using  a  motor  placed  on  the  platform  of 
the  car  or  locomotive  was  adhered  to.  This  was  almost  necessary, 
since  the  performance  of  the  motors  was  so  poor  that  it  was 
absolutely  essential  to  keep  a  close  watch  on  the  motor  operation, 

71 


72 


THE  ELECTRIC  RAILWAY 


especially  of  the  commutator  and  brushes.  It  was  considered 
the  best  practice  to  shift  the  brushes  to  give  good  commutation; 
and  if  the  car  was  reversed,  a  considerable  brush  displacement 
was  called  for. 

With  the  road  installed  in  Richmond  in  1888  by  Frank  J. 
Sprague  came  the  recognition  that  the  railway  motor  is  a  special 
piece  of  machinery,  and  should  be  designed  to  perform  its  work 
in  the  best  possible  manner.  In  this  installation  the  motors 
were  hung  on  the  car  axles,  and  were  inaccessible  from  the  floor 
of  the  car  for  constant  inspection  and  adjustment.  Since  these 
motors  were  designed  to  be  reversible,  it  was  necessary  to  place 
the  brushes  in  the  neutral  position,  making  no  allowance  for 
shifting  them  to  obtain  good  commutation.  This  practice  has 


FIG.  36. — Sprague  motor. 

This  is  the  type  of  motor  which  was  used  on  the  Richmond  road  in  1888. 
forms  were  used,  but  the  general  appearance  of  all  was  quite  similar. 


Several  different 


persisted  to  the  present  time,  and  the  design  of  modern  motors 
has  always  been  made  with  this  feature  as  a  necessary  detail. 

The  early  motors  were  all  bipolar,  following  the  stationary 
practice  of  that  time.  It  was  not  until  about  ten  years  after  the 
first  electric  railways  were  operated  that  it  was  considered  more 
economical  to  use  multipolar  designs,  in  order  to  get  better 
distribution  of  the  active  material  and  to  obtain  improved  per- 
formance. When  it  was  found  possible  to  build  multipolar  rail- 
way motors,  an  attempt  was  made  to  use  a  comparatively  large 
number  of  poles.  This  arrangement  was  also  abandoned  in 
favor  of  motors  with  four  poles,  which  number  has  become  standard 
for  all  direct-current  railway  motors  of  the  ordinary  types. 

The  first  railway  motors,  being  a  direct  adaptation  of  the 
stationary  types,  were  entirely  open.  While  this  type  of  ma- 
chine had  better  facilities  for  getting  rid  of  the  heat  generated  by 
the  losses,  the  exposure  of  an  open  motor  under  a  car,  to  all 


RAILWAY  MOTOR  CONSTRUCTION  73 

sorts  of  dirt,  mud,  and  water,  led  to  grounding  of  the  insulation, 
pitting  of  the  commutators,  and  rapid  destruction  of  the  bear- 
ings. The  logical  remedy  was  to  totally  enclose  the  working 
parts  of  the  motor,  extending  the  field  frame  to  make  a  casing 
around  the  field  and  armature.  The  first  attempts  of  this  sort 
did  not  aim  at  total  enclosure  of  the  working  parts.  While 
the  partial  enclosing  did  some  good,  there  was  still  difficulty 
from  splashing  water  and  dust.  The  successive  designs  went 
further,  until  no  openings  whatever  to  the  interior  of  the  motor 
were  left.  Access  to  the  commutator  was  had  by  means  of  a 
hand-hole  with  removable  cover;  but  since  by  that  time  the 
commutation  had  been  improved  to  a  point  where  constant 
inspection  was  unnecessary,  this  caused  no  disadvantage. 

Armature  Construction. — The  early  armatures  were  of  the 
smooth  core,  hand  wound  drum  type,  usually  with  one  turn  per 
commutator  bar,  with  either  a  lap  or  a  ring  winding.  Such  a 
construction  requires  as  many  brush  arms  as  the  motor  has 
poles.  It  was  found  that  by  the  use  of  the  two-circuit  wave  wind- 
ing but  two  brush  arms  were  required,  irrespective  of  the  number  of 
poles  on  the  motor.  This  was  an  important  improvement, 
since  it  became  possible  to  place  both  brush  arms  on  the  upper 
part  of  the  commutator,  where  they  could  be  easily  inspected 
through  the  hand-hole.  Better  knowledge  of  the  phenomena  of 
commutation  led  to  the  use  of  slotted  cores  for  the  armatures. 
This  was  more  of  an  advance  than  may  appear  at  first,  for  the 
heavy  torque  required  at  starting  had  the  effect  of  stripping 
the  windings  off  the  smooth  cores.  With  the  slotted  type,  the 
wires  had  a  solid  wall  of  iron  against  which  to  exert  the  push. 
The  knowledge  of  commutation  also  made  it  possible  to  wind 
the  armatures  with  more  than  one  turn  per  commutator  bar, 
thus  making  a  cheaper  and  more  rigid  construction,  and  facilita- 
ting repairs. 

These  changes  in  armature  construction  were  coincident 
with  improvements  in  the  brushes  and  brush  rigging.  The 
early  machines  used  brushes  of  leaf  copper,  such  as  are  some- 
times employed  at  the  present  time  on  electrolytic  machines. 
The  use  of  brushes  of  this  type,  with  inherently  low  resistance, 
made  a  small  number  of  turns  between  bars  necessary  to  prevent 
excessive  sparking.  In  the  history  of  the  Richmond  road, 
brushes  of  solid  bronze  were  used  at  one  period.  Replacement 


74  THE  ELECTRIC  RAILWAY 

of  all  these  types  of  brush  with  those  of  carbon  made  possible 
the  changes  in  armature  design  noted  above. 

Armature  Speeds. — In  nearly  all  of  the  pioneer  designs  of 
railway  motors,  the  armatures  were  of  large  diameter.  This 
construction  was  adopted  to  get  the  necessary  high  peripheral 
speed  without  having  an  extremely  great  angular  velocity. 
Even  with  the  large  armatures  the  speeds  were  excessive  in 
many  instances.  The  use  of  multipolar  motors  made  possible  a 
lower  peripheral  speed,  and,  at  the  same  time,  a  reduction  in 
speed  of  rotation.  This  effect  was  aided  by  lengthening  the 
core  somewhat  parallel  to  the  shaft.  The  large  diameter  arma- 
ture, especially  when  rotating  at  a  high  speed,  possessed  a 
great  deal  of  inertia.  We  have  already  seen  that  the  inertia 
of  the  rotating  parts  of  the  equipment  is  a  comparatively  im- 
portant part  of  the  total  for  a  moving  car.  The  still  larger 
amount  of  inertia  caused  the  consumption  of  additional  energy, 
and  considerable  extra  brake  wear,  besides  increasing  the  time 
for  stopping  the  cars. 

In  most  of  the  early  motors,  the  armature  speeds  were  so 
high  that  single-reduction  gears  could  not  be  used,  and  it  was 
necessary  to  have  back-geared  or  double-reduction  motors. 
This  caused  an  extra  loss,  and  an  added  complication  that  did 
not  seem  warranted.  The  slower  armature  speeds  obtained 
in  the  later  designs  brought  at  the  same  time  the  single-reduction 
gearing  which  has  persisted  to  the  present  time  except  for 
certain  large  locomotive  motors. 

Field  Frames. — Motors  of  the  old  horseshoe  type  were  almost 
invariably  made  with  field  yokes  of  wrought  iron.  While  this 
material  has  excellent  electrical  properties,  it  is  entirely  too 
expensive  for  use  on  a  large  scale,  as  in  railway  motors.  The 
alternative  material  which  was  developed  in  the  early  history  of 
electric  motors  is  cast  iron.  This  is  much  cheaper,  but  requires 
approximately  twice  the  weight  for  the  same  field  strength. 
On  the  other  hand,  it  lends  itself  better  to  the  totally  enclosed 
designs  which  were  coming  into  vogue  at  the  time  it  was  intro- 
duced. Cast  iron,  in  its  turn,  was  found  too  heavy,  and  in  some 
cases  not  strong  enough.  It  was  gradually  superseded  by  cast 
steel,  which  has  been  the  accepted  material  for  railway  motor 
frames  for  over  fifteen  years.  Cast  steel  is  more  expensive  per 
unit  of  weight  than  cast  iron;  but  its  superior  magnetic  properties 


RAILWAY  MOTOR  CONSTRUCTION  75 

allow  the  manufacture  of  a  frame  weighing  about  half  that  for  a 
cast-iron  one,  and  at  approximately  the  same  cost. 

If  there  is  a  sufficient  .demand  for  motors  of  a  certain  type,  it  is 
possible  that  cast  steel  may  in  its  turn  be  superseded  by  frames 
of  rolled  and  pressed  open-hearth  steel.  Although  the  first  cost 
of  a  pressed-steel  frame  is  exceedingly  high,  the  manufacture  of 
large  quantities  of  a  certain  single  design  will  make  it  an  active 
competitor  of  the  cast  steel.  One  design  has  already  been  made 
using  pressed  steel,  and  which  is  superior  in  many  ways  to  the 
ordinary  type  of  cast-steel  motor. 

The  changes  outlined  above  mark  the  development  of  the  rail- 
way motor  from  a  crude  device,  upon  which  little  reliance  could 
be  placed,  to  one  that  can  be  used  without  difficulty,  and  will 
perform  its  work  satisfactorily  under  the  severe  conditions  of 
service  inherent  to  railway  operation.  The  structural  develop- 
ment outlined  was  carried  along  with  an  improvement  of  con- 
struction details  both  electrical  and  mechanical.  The  result  is 
an  increase  in  efficiency  from  quite  low  values,  to  fairly  high  ones 
over  the  entire  operating  range.  In  a  railway  system,  efficiency 
of  the  traction  motor  is  but  a  small  item;  but  the  saving  in  cost 
due  to  the  increase  in  efficiency  is  worth  considerable  to  the 
railway  operator,  since  it  has  come  with  other  improvements  of  a 
desirable  nature. 

Modern  Direct-Current  Railway  Motors. — The  development 
we  have  just  traced  has  been  entirely  in  the  direct-current  series 
motor.  The  greater  part  of  it  took  place  prior  to  the  year  1893; 
since  that  time  the  changes  have  been  more  in  the  nature  of  minor 
refinements  than  in  radical  developments. 

Modern  Motor  Frames. — The  frames  of  modern  motors  are 
made  of  cast  steel,  and  include  the  magnetic  circuit  of  the  field, 
with  the  protecting  casing.  There  are  two  types  of  frame  in 
general  use — solid  and  split.  The  split  frames  are  the  earlier 
development.  It  was  formerly  the  universal  practice  to  inspect 
the  motors  without  removing  them  from  the  car  axles.  This 
is  done  in  one  of  two  ways.  The  motor  is  split  in  a  horizontal 
plane  through  the  shaft  in  such  a  manner  that  the  lower  half 
can  be  dropped  down,  thus  permitting  inspection  from  a  pit 
beneath  the  track;  or  else  the  upper  half  can  be  raised,  allowing 
inspection  on  the  shop  floor  after  the  truck  has  been  run  out 
from  under  the  car.  This  latter  method  was  used  only  on  a  few 


76 


THE  ELECTRIC  RAILWAY 


of  the  largest  systems,   the  former  being  much  more  widely 
employed. 

With  the  refinements  which  have  been  made  in  modern  motors, 
the  need  for  inspection  has  diminished,  so  that  it  is  possible  to 
make  a  far  greater  mileage  between  overhaulings  of  the  motors 
than  previously.  This  has  made  possible  the  use  of  motors  with 
solid  frames,  the  armatures  being  removed  from  the  end.  This 
latter  construction  is  more  rigid  and  somewhat  cheaper;  but  it 
makes  it  impossible  to  remove  an  armature  unless  the  entire 
motor  is  first  taken  off  the  truck.  To  determine  the  clearance 
between  the  armature  and  poles,  it  is  customary  to  have  small 

hand-holes  for  inspection  in 
the  lower  portion  of  the 
motor  case. 

The  choice  of  solid  or  split 
frames  depends  largely  on 
the  shop  equipment  avail- 
able for  handling  the  motors. 
In  some  small  shops  it  is 
quite  difficult  to  remove  and 
replace  the  armatures  of 
solid^frame  motors;  but  in 
the  larger  shops,  especially 
those  equipped  with  cranes, 
the  employment  of  this  type 
has  proved  entirely  saisfactory;  and  their  use  seems  to  be  grow- 
ing at  the  present  time. 

In  the  first  designs  of  railway  motors,  the  poles  were  made 
integral  with  the  main  horseshoe  forgings  for  the  field.  This  was 
fairly  successful,  since  a  high-grade  magnetic  material  of  prac- 
tically uniform  permeability  was  used.  The  first  machines  with 
cast-iron  frames  had  the  poles  cast  in  the  frames.  This  design 
was  not  successful,  since  neither  the  control  over  the  quality  of 
the  metal,  nor  the  dimensions  of  the  poles,  was  complete.  In  a 
few  types,  an  attempt  was  made  to  correct  this  trouble  by  build- 
ing up  poles  of  laminated  steel,  and  casting  them  into  the  motor 
frame.  While  this  was  an  improvement,  it  did  not  meet  all  the 
demands  of  a  satisfactory  pole  structure.  In  all  modern  motors 
the  poles  are  made  of  steel  laminations,  built  up  and  riveted 
together.  They  are  fastened  into  the  field  frame  with  bolts,  and 


FIG.  37. — Modern  direct-current  rail- 
way motor. 

This  is  the  solid-frame  type  of  motor.  The 
armature  is  removed  by  taking  off  the  end-bell 
after  the  motor  has  been  removed  from  the  car. 
The  axle  gear  and  the  gear  case  are  not  shown. 


RAILWAY  MOTOR  CONSTRUCTION 


77 


are  so  designed  that  they  may  be  removed  without  taking  the 
armature  out  of  the  case. 

The  use  of  the  laminated  pole  makes  it  possible  to  shape  the 
pole  tips  to  aid  commutation,  and  they  can  be  properly  spaced 
in  the  frame  to  ensure  correct  alignment.  This  feature,  although 
perhaps  not  fully  appreciated,  is  one  of  the  factors  in  the  splendid 
performance  of  modern  direct-current  motors. 

Use  of  Interpoles. — Within  the  past  few  years  the  use  of 
interpoles  has  become  quite  general.  Of  all  types  of  commutator 
electric  motors,  the  series  machine  has  the  least  inherent  tendency 
to  spark,  since  the  field  strength  automatically  increases  with  the 
armature  current.  The  sud- 
den and  heavy  overloads,  how- 
ever, make  the  very  best  com- 
mutation a  necessity  for  con- 
tinued successful  operation. 
In  all  cases  where  constant 
attention  cannot  be  given  the 
commutator,  the  destructive 
results  of  sparking  are  cumula- 
tive; and  even  though  the 
sparking  of  well-designed  non- 
interpole  railway  motors  was 
formerly  considered  negligible, 
the  wear  of  both  commutator 
and  brushes  is  considerable. 
The  use  of  interpoles  has  re- 
duced sparking  to  a  point  where  it  is  practically  absent;  and 
with  its  decrease  a  great  gain  has  been  realized  in  the  life  of 
commutators  and  brushes. 

In  form  the  interpoles  are  practically  the  same  as  those  for 
stationary  direct-current  machinery.  The  turns  are,  so  far  as 
possible,  concentrated  near  the  armature  surface,  to  increase 
their  effectiveness.  The  supporting  cores  are  of  steel,  bolted  into 
the  field  frame  between  the  main  poles.  The  inter  pole  coils  are 
connected  directly  in  series  with  the  armature  and  field  windings, 
and  are  arranged  so  that  they  may  be  reversed  along  with  the 
armature,  in  order  that  the  current  through  the  commutating 
coils  may  be  in  the  proper  direction  to  assist  the  commutation 
and  not  hinder  it. 


FIG.  38. — Arrangement  of  interpoles. 

The  main  poles,  a,  and  the  interpoles,  b, 
have  windings  which  are  placed  in  series  with 
the  armature.  Usually  the  main  field  winding 
is  reversed  to  change  the  direction  of  rotation. 


78  THE  ELECTRIC  RAILWAY 

Modern  Armature  Construction. — The  armatures  of  modern 
motors  are  invariably  of  the  slotted  drum  type,  and  are  wound 
with  two  complete  coils  per  slot.  The  early  armatures  of  this 
class  were  designed  with  a  comparatively  large  number  of  small 
slots,  each  with  one  or  two  single  coils  in  it.  This  practice  causes 
weak,  narrow  teeth,  and  is  wasteful  of  space,  since  the  major  coil 
insulation  must  necessarily  be  of  a  definite  thickness  whether 
one  or  a  number  of  separate  coils  are  assembled  together.  Inci- 
dentally the  cost  of  punching  the  iron  with  a  large  number  of 
teeth  is  greater,  and  the  commutation  is  poorer.  Modern 
practice  is  to  include  from  three  to  five  single  coils  in  each  com- 
plete coil,  so  that  the  total  number  of  slots  is  considerably  less  than 
in  the  early  armatures,  even  though  the  number  of  commutator 
bars  has  been  increased. 

In  some  motors  the  armature  punchings  are  assembled 
directly  on  the  shaft,  and  in  others  they  are  mounted  on  a  spider 
of  cast  iron.  In  the  larger  machines  the  use  of  the  spider  is 
universal.  Its  employment  depends  on  the  amount  of  iron  which 
needs  to  be  left  back  of  the  teeth  for  carrying  the  flux,  and  on  the 
arrangements  made  for  ventilation. 

Armature  windings  of  direct-current  railway  motors  are  almost 
invariably  of  the  two-circuit  type.  The  use  of  two-circuit  wind- 
ings, as  has  already  been  stated,  results  in  the  need  for  only  two 
brush  arms,  no  matter  how  many  poles  the  motor  has.  On  the 
other  hand,  if  the  current  capacity  is  large,  a  brush-arm  can 
be  supplied  for  each  pole  of  the  motor,  thus  making  possible  a 
short  commutator.  The  maximum  currents  to  be  handled  with 
direct-current  motors  are  usually  well  within  the  limits  of  the 
two-circuit  winding. 

Armature  coils  are  made  of  wire  only  in  the  small  sizes.  For 
the  larger  motors,  strap-wound  coils  are  the  universal  practice. 
The  strap  gives  a  better  space-factor — i.e.,  the  proportion  of  the 
slot  occupied  by  copper  is  greater,  and  that  taken  up  by  insula- 
tion is  less.  Generally,  the  individual  armature  coils  are  wound 
complete  in  one  piece ;  but  in  some  types  the  coils  are  separated  into 
two  parts,  and  are  connected  together  at  the  back  end  of  the 
armature.  This  makes  replacement  of  damaged  coils  easier,  but 
increases  the  number  of  soldered  joints. 

Commutator  Construction. — Modern  commutators  are  gener- 
ally built  of  rolled  or  drop-forged  copper.  Uniformity  of  the 
surface  has  much  to  do  with  long  life  of  the  commutator  and 


RAILWAY  MOTOR  CONSTRUCTION  79 

brushes  in  service.  Another  factor  is  the  material  employed 
for  insulation  between  bars.  Although  a  number  of  materials 
have  been  used,  the  only  one  which  has  been  satisfactory  is 
mica.  At  the  present  time  it  is  exceedingly  difficult  to  obtain 
mica  of  uniform  quality,  and  in  consequence  the  practice  has 
been  adopted  of  using  insulation  built  up  from  small  sheets  of 
this  material  held  together  with  some  form  of  binder,  such  as 
shellac.  To  get  good  service  from  a  commutator,  the  insula- 
tion and  the  copper  must  wear  down  at  the  same  rate.  If  the 
mica  is  too  soft,  it  will  wear  away  faster  than  the  copper,  and 
leave  low  spots  at  the  edges  of  the  bars.  On  the  contrary,  if 
the  mica  is  too  hard,  it  will  not  wear  away  as  rapidly  as  the 
copper.  The  result  will  be  that  the  brushes  will  have  a  tend- 
ency to  jump  away  from  the  surface  of  the  commutator,  causing 
sparking  and  flashing  which  will  conduce  to  further  pitting  and 
wearing  down  of  the  copper,  until  turning  is  necessary.  Prac- 
tically all  the  mica  which  is  available  for  commutator  insula- 
tion at  the  present  day  is  harder  than  the  copper  surface,  giving 
the  latter  effect.  The  remedy  for  this  is  the  practice,  which  is 
being  quite  generally  adopted,  of  "  under  cut  ting"  the  mica,  or 
removing  it  to  a  depth  of  about  Jfg  m-  below  the  surface. 
This  permits  the  brushes  to  bear  evenly  on  the  commutator, 
and  allows  uniform  wear  of  the  copper.  With  the  aid  of  corn- 
mutating  poles  and  undercut  mica  the  commutation  of  modern 
motors  is  well-nigh  perfect. 

Motor  Lubrication. — It  is  in  the  mechanical  parts  of  the 
motor  that  the  most  radical  changes  have  been  made  since 
the  beginnings  of  electric  railway  operation.  In  the  early 
machines,  lubrication  was  commonly  effected  with  grease. 
Grease  as  a  lubricant  is  theoretically  inefficient,  since  it  re- 
quires the  bearing  to  overheat  before  acting.  It  has  been  re- 
placed by  the  use  of  oil,  carried  to  the  rotating  part  by  capillary 
attraction  through  the  medium  of  wool  waste,  which  rubs 
against  the  shaft,  and  thus  ensures  a  constant  supply  of  oil  under 
all  conditions.  Both  armature  bearings  and  axle  bearings  are 
lubricated  in  the  same  manner. 

Bearing  Housings  and  Bearings. — As  the  early  motors  were 
of  the  open  type,  there  was  little  difficulty  in  removing  the 
armatures  for  inspection  or  for  repair.  When  the  enclosed 
motors  became  standard,  provision  for  removing  the  armatures 
was  made  by  splitting  the  frames,  as  already  explained.  With 


80 


THE  ELECTRIC  RAILWAY 


the  modern  solid-frame  motors,  the  armatures  must  be  removed 
from  the  ends  of  the  casing.  To  do  this,  the  opening  in  the 
end  of  the  frame  must  be  at  least  as  large  as  the  diameter  of 
the  armature.  The  accepted  method  of  closing  this  opening 
is  to  use  a  bearing  bracket,  turned  to  fit  a  bored  hole  in  the 
frame,  and  containing  the  bearing  and  bearing  housing,  to- 
gether with  the  oil  receptacle.  The  same  type  of  end  bracket 
has  been  adopted  with  split-frame  motors,  on  account  of  the 
rigid  support  it  gives  the  bearing,  and  its  excellent  arrangement 
for  oiling. 

The  bearings  proper  are  made  of  brass  or  bronze,  with  the 
wearing  surface  of  babbitt  metal.  This  construction  is  good, 
since  the  use  of  a  soft  metal  reduces  the  friction  to  a  minimum 
under  normal  conditions;  and  if  anything  happens  to  melt  out 
the  babbitt,  the  bronze  itself  furnishes  a  good  bearing  to  run  on 
until  the  motor  can  be  removed  from  the  car  at  the  end  of  the 
trip.  Without  such  a  safeguard  the  melting  of  the  babbitt 
would  cause  the  armature  to  strike  the  pole  faces,  resulting  in 
damage  to  the  winding  and  possibly  destruction  of  the  core 
itself. 

Ventilation  of  Motors. — The  oldest  railway  motors,  being 
open,  were  ventilated  entirely  by  natural  circulation  of  the  sur- 


FIG.  39. — Method  of  forced  ventilation. 

The  air  is  circulated  through  the  motor  case  by  means  of  fans  carried  on  the  armature.  A 
number  of  other  arrangements  of  air-paths  are  in  use  to  obtain  a  passage  of  air  through  the 
motor  case. 

rounding  air.  With  the  advent  of  the  enclosed  motor,  a  different 
condition  was  confronted.  The  outside  air  no  longer  had 
access  to  the  armature,  commutator  and  field  coils;  but  all  the 
heat  generated  had  to  be  transferred  to  the  frame  and  dissipated 
from  the  outside  surface  of  the  case.  The  result  was  that  the 
capacity  of  a  motor  of  given  weight  was  much  smaller  than  in 


RAILWAY  MOTOR  CONSTRUCTION  81 

the  case  of  the  corresponding  open  machine.  But  it  has  been 
found  necessary,  on  account  of  the  bad  effects  of  dust  and 
moisture,  to  keep  the  motors  almost  completely  enclosed.  A 
number  of  years  ago  an  attempt  was  made  to  force  air  into 
the  motor  by  means  of  ducts  leading  to  the  front  of  the  car. 
This  was  not  entirely  successful;  but  it  led  the  way  to  the  use 
of  fans  on  the  motor  armature,  by  means  of  which  a  circulation 
is  established,  drawing  air  in  from  the  outside,  and  passing  it 
through  the  motor,  finally  discharging  it  again.  By  this  method, 
shown  in  Fig.  39,  the  temperature  of  the  motor  may  be  reduced 
materially  for  the  same  load,  or  the  rating  of  a  given  motor  may 
be  increased.  The  result  is  to  lighten  the  equipment. 

In  the  large  locomotive  motors  such  ventilation  would  not 
be  sufficient,  especially  since  the  greatest  generation  of  heat 
occurs  when  starting.  At  this  time  the  efficiency  of  any  fan 
driven  by  the  armature  is  least,  and  the  cooling  effect  small, 
since  the  speed  is  low.  To  give  an  adequate  supply  of  cooling 
air  to  such  motors,  they  are  provided  with  ventilating  ducts, 
the  air  being  furnished  from  an  independent  motor-driven  blower 
located  in  the  cab. 

Single-Phase  Commutator  Motors. — In  the  case  of  single- 
phase  motors,  the  field  flux  is  alternating.  A  solid  field  structure 
is  inadmissible,  and  it  is  necessary  to  provide  a  complete  lami- 
nated core  for  the  magnetic  flux.  This  leads  to  a  quite  different 
arrangement  from  that  of  the  standard  direct-current  motors. 
The  field  is  built  up  of  a  set  of  punchings,  which  are  held  rigidly 
in  a  frame  of  cast  steel  that  also  serves  as  the  enclosing  case  of 
the  motor.  The  poles  are  made  integral  with  the  core,  for  it  is 
impossible  to  remove  them  on  account  of  the  compensating 
winding. 

The  field  coils  of  alternating-current  series  motors  are  not 
essentially  different  from  those  of  direct-current  motors,  except 
that  they  have  less  turns.  The  compensating  windings,  instead 
of  being  concentrated,  as  in  the  direct-current  interpoles,  are 
distributed  over  nearly  the  entire  pole-face.  By  this  means  the 
neutralizing  ampere  turns  are  placed  very  near  the  armature 
conductors  whose  inductance  it  is  desired  to  oppose,  and  their 
effectiveness  is  increased. 

On  account  of  the  compensating  winding,  it  is  not  possible  to 
split  the  frame;  and,  since  the  majority  of  single-phase  motors 
are  of  comparatively  large  rating,  and  are  used  on  roads  with 

6 


82 


THE  ELECTRIC  RAILWAY 


adequate  shop  equipment,  there  is  not  a  great  demand  for  that 
construction.  In  most  modern  machines,  the  external  appear- 
ance is  not  essentially  different  from  that  of  direct-current  motors 
of  similar  capacity. 

The  armatures  of  alternating-current  series  motors  are  very 
nearly  the  same  as  those  for  direct-current  motors,  the  principal 
apparent  difference  being  the  greater  number  of  commutator 
bars  on  the  former.  In  the  type  manufactured  in  the  United 
States,  there  is  a  difference,  not  readily  discernible,  due  to  the 
interposition  of  resistance  leads  between  the  armature  coils  and 
the  commutator.  These  leads  are  placed  in  the  bottoms  of  the 
slots  in  the  smaller  sizes  of  motors;  and  in  the  larger  ones  are 


FIG.  40. — Interior  of  single-phase  series  motor. 

The  pole  faces  are  slotted,  and  have  the  conductors  of  the  compensating  winding  em- 
bedded in  them. 

placed  in  the  core  in  separate  slots  located  beneath  the  path 
of  the  flux.  This  method  of  construction  makes  repairs  and 
replacements  comparatively  easy. 

In  distinction  to  the  direct-current  armatures,  those  of  single- 
phase  motors  are  ordinarily  lap  wound.  Since  there  is  a  possi- 
bility of  uneven  distribution  of  the  magnetic  flux,  due  to  in- 
equalities in  the  air  gap,  it  is  customary  to  supply  them  with 
balancing  rings  such  as  are  used  on  large  generators.  The  use 
of  these  rings  permits  equalizing  currents  to  flow  in  the  armature, 
thus  compensating  for  variations  in  the  magnetic  strength  of 
different  poles. 

The  use  of  lap- wound  armatures  makes  obligatory  the  use  of  as 
many  brush  arms  as  there  are  poles.  In  order  to  improve  the 
performance  of  the  motors,  there  is  a  tendency  to  increase  the 


RAILWAY  MOTOR  CONSTRUCTION  83 

number  of  poles,  which  requires  an  additional  number  of  brush 
arms.  For  this  reason  it  is  somewhat  more  difficult  to  maintain 
the  brushes  on  single-phase  motors. 

None  of  the  purely  mechanical  parts  of  the  alternating-current 
series  motors  are  essentially  different  in  any  particular  from  those 
of  direct-current  motors.  In  fact,  the  external  appearance  is 
nearly  identical  for  the  two  types  of  machines.  Since  the  alternat- 
ing-current motors  are  used  to  a  considerable  extent  on  large 
locomotives,  the  design  of  individual  units  may  lead  to  a  material 
difference  in  appearance. 

Induction  Motors. — The  design  of  induction  motors  for  railway 
service  calls  for  more  radical  departures  from  the  ordinary  direct- 
current  designs  than  is  the  case  with  the  series  motor.  The  field 
or  primary  winding  is  usually  placed  on  the  stator;  but  it  must  be 
distributed,  and  resembles  an  armature  winding.  This  calls  for  a 
different  type  of  construction.  The  enclosing  frame,  however, 
may  be  made  to  resemble  that  of  the  direct-current  motor  quite 
closely,  and  the  mechanical  parts  may  be  the  same. 

The  secondary  is  generally  made  the  rotor;  and,  for  the  forms 
ordinarily  used  in  traction  work,  the  winding  is  of  the  definite 
type,  similar  to  that  of  the  primary.  There  is  this  essential 
difference :  no  commutator  is  required,  and  the  ends  of  the  wind- 
ings are  brought  out  to  collector  rings,  through  which  the  current 
is  led  to  the  resistors  by  means  of  brushes.  The  secondary  has 
no  connection  whatever  with  the  supply  circuit,  and  can  be 
wound  for  any  convenient  potential.  The  secondary  windings 
are  nearly  always  made  three-phase,  since  this  allows  of  the 
minimum  number  of  rings  and  brushes. 

The  location  of  the  collector  rings  is  a  matter  of  some  impor- 
tance. If  the  size  of  the  motor  is  not  excessive,  the  rings  can  be 
located  inside  the  frame,  in  a  position  similar  to  that  of  the  com- 
mutator in  a  series  motor.  If  the  capacity  of  the  motor  is  large, 
it  may  be  difficult  to  find  room  for  the  collector.  In  some 
designs  it  is  mounted  inside  the  spider;  in  at  least  one,  the  leads 
from  the  winding  are  taken  through  the  bearing  in  a  duct  bored 
in  the  shaft,  the  collector  being  placed  outside  the  crank.  While 
this  may  be  considered  an  extreme  design,  it  was  necessitated  by 
the  demands  made  on  the  motor  for  space. 


CHAPTER  V 
CONTROL  OF  RAILWAY  MOTORS 

Need  for  Control. — If  an  electric  motor  of  any  type,  with  its 
armature  at  rest,  were  connected  directly  to  the  line,  an  excessive 
current  would  flow,  limited  only  by  the  impedance  of  the  motor 
and  the  supply  circuit.  In  case  the  protective  devices  failed 
to  open  the  circuit,  the  torque  produced  would  in  general  be  so 
great  as  to  slip  the  driving  wheels;  or,  failing  to  do  that,  to  start 
the  train  with  a  severe  jerk.  Since  a  fairly  uniform  acceleration 
of  moderate  amount  is  desirable,  some  form  of  control  which 
limits  the  torque  to  a  proper  value  is  an  absolute  essential  to 
satisfactory  operation. 

Available  Methods. — There  are  two  general  methods  for 
obtaining  the  desirable  changes  in  characteristics,  which  are 
applicable  to  nearly  all  types  of  electric  motors: 

1.  Variations  in  potential. 

2.  Changes  in  relative  strength  of  armature  and  field. 

For  certain  types  of  alternating-current  motors,  the  characteris- 
tics may  be  varied  by  the  following  additional  methods: 

3.  Changes  in  the  number  of  poles. 

4.  Changes  in  frequency. 

Change  of  Potential. — The  effect  of  changes  in  the  terminal 
potential  is  different  with  various  types  of  motors.  In  the  case  of 
"constant  field"  machines,  such  as  the  direct-current  shunt 
motor,  or  the  alterating-current  induction  motor,  a  change  of 
potential  at  the  terminals  varies  the  field  or  magnetizing  current 
and  hence  affects  the  field  flux.  The  variation  in  the  flux  cor- 
responding to  a  given  change  in  the  terminal  e.m.f .  depends  on  the 
characteristic  of  the  magnetic  circuit;  and  in  general  is  different 
for  individual  machines.  If  the  magnetic  circuit  is  practically 
unsaturated,  as  in  most  alternating-current  induction  motors, 
the  torque  produced  by  a  given  current  varies  approximately  as 
the  square  of  the  e.m.f.  In  this  type  of  motor  a  reduction  in  the 
terminal  potential  has  a  comparatively  small  effect  on  the  speed, 

84 


CONTROL  OF  RAILWAY  MOTORS  85 

that  being  determined  principally  by  the  frequency  of  the  supply 
circuit. 

In  the  direct-current  shunt  motor,  a  change  of  potential  will 
not  have  quite  so  much  effect  on  the  torque  as  in  the  induction 
motor,  since  the  field  is  normally  saturated  to  some  extent;  but 
the  change  in  torque  will  be  considerably  greater  than  in  direct 
proportion  to  the  applied  potential.  At  the  same  time  the  speed 
will  be  varied  somewhat  by  a  change  in  e.m.f.  These  effects 
may  be  obviated  by  placing  the  field  winding  in  a  separate 
circuit  and  keeping  it  connected  to  a  source  of  constant 
potential.  The  field  flux  will  then  remain  constant,  and  the 
torque  will  be  the  same  for  any  value  of  terminal  e.m.f.  The 
speed  will  vary  practically  in  proportion  to  the  applied  potential. 

In  the  series  motor,  a  change  in  the  terminal  e.m.f.  has  no 
effect  on  the  field  flux  for  a  given  current;  but  the  speed  will 
vary  nearly  in  proportion  to  the  e.m.f.  applied  to  the  terminals 
(see  Chapter  III). 

Methods  of  Potential  Variation. — The  possible  methods  by 
which  the  potential  may  be  varied  in  railway  motor  control 
are: 

1.  Change  of  e.m.f.  supplied  the  motor. 

2.  Combinations  of  motors  (e.g.,  series  and  parallel). 

3.  Insertion  of  resistance  in  motor  circuits. 

Changing  the  e.m.f.  supplied  the  motor  is  difficult  of  ac- 
complishment in  ordinary  direct-current  equipments,  since 
some  form  of  rotating  apparatus  is  necessary  to  produce  the 
desired  result.  Although  this  method  has  been  suggested  in 
one  type  of  control,  it  has  never  been  introduced  practically. 
For  alternating-current  motors,  changes  in  potential  may  be 
easily  accomplished  by  taking  taps  from  a  transformer  or  an 
auto-transformer  to  give  the  desired  values. 

A  simple  and  efficient  means  of  varying  the  e.m.f.  applied  at 
the  motor  terminals  is  available  when  an  equipment  consists  of 
two  or  more  motors,  by  placing  them  either  in  series  or  in  parallel 
with  one  another.  Two-motor  equipments  can  thus  be  arranged 
to  take  full  potential  and  half  potential  at  their  terminals;  three- 
motor  equipments  (if  such  were  used)  could  have  full  potential  and 
one-third  potential ;  and  four-motor  equipments  full,  one-half  and 
one-quarter  potential.  This  method  of  reducing  the  pressure  is 
used  in  nearly  all  direct-current  equipments.  When  this  method 
of  reducing  potential  is  used,  it  is  necessary  that  all  the  motors  in 


86 


THE  ELECTRIC  RAILWAY 


600 


the  combination  have  identical  characteristics,  since  otherwise 
they  will  not  divide  the  line  e.m.f .  equally  when  in  series,  or  the 
current  equally  when  in  parallel.  No  troubles  of  this  sort  are 
to  be  anticipated  from  modern  motors  as  received  from  the 
manufacturer,  provided  only  machines  of  the  same  type  and 
rating  are  used  together.  In  case  motors  have  been  repaired 
by  unskilled  workmen,  it  may  be  necessary  to  test  them  in 
order  to  be  sure  that  the  performance  has  not  been  changed.  If 
these  precautions  be  taken,  the  motors  will  divide  the  pressure 
equally  among  themselves  at  all  loads  when  in  series  (see  Fig.  41). 
Since  the  current  taken  by  motors  in  series  is  the  same,  the  load 
imposed  on  them  must  in  that  case  be  equal.  The  only  con- 
dition which  can  then  cause  trouble 
is  that  one  motor  may  revolve  faster 
than  the  other,  due  to  slipping  of  the 
wheels.  When  this  happens,  the 
motor  whose  driving  wheels  are  slip- 
ping will  develop  a  greater  counter 
e.m.f.  than  the  other,  which  will  then 
tend  to  run  at  a  reduced  speed,  until 
it  finally  stops,  the  first  motor  revolv- 
ing with  but  a  small  load  due  to  the 
sliding  friction  of  the  wheel  on  the  rail. 
To  overcome  this  difficulty  the  motors 
must  be  stopped  and  the  rail  sanded. 
With  direct-current  motors,  the 
insertion  of  series  resistance  has  a 

similar  effect  to  a  forced  reduction  of  potential.  Since  such  an 
added  resistance  increases  the  IR  drop,  the  amount  of  reduc- 
tion in  pressure  at  the  motor  terminals  varies  directly  wtih 
the  current.  A  resistance  which  will  reduce  the  terminal  po- 
tential of  a  motor  to  a  low  value -with  a  heavy  current  will  have 
but  little  effect  on  it  at  light  loads  (see  Fig.  21).  The  effect 
of  series  resistance  is  quite  different  in  the  various  types  of  direct- 
current  motors.  In  the  series  motor  it  serves  merely  to  reduce 
the  pressure  at  the  armature  terminals,  without  affecting  the 
field  strength  for  a  given  armature  current;  but  in  the  shunt 
motor,  it  reduces  the  field  current  as  well.  The  result  in  this 
case  is  similar  to  that  already  noted  for  forced  changes  in  motor 
potentials;  and,  if  it  is  desired  to  control  the  shunt  motor  in 
this  manner,  the  resistance  should  be  placed  in  the  arma- 


Ho+or 
No.  2 


FIG.  41. — Division  of  e.m.f. 
with  motors  in  series. 


CONTROL  OF  RAILWAY  MOTORS 


87 


ture  circuit  alone,  the  field  being  permanently  connected  to  the 
line. 

A  reduction  in  the  potential  supplied  an  induction  motor- 
affects  it  in  much  the  same  way  as  with  the  shunt  motor.  Since 
the  armatures  of  several  machines  cannot  be  placed  in  series,  as 
with  direct-current  shunt  motors,  this  method  of  control  has 
but  little  application. 

Changes  in  Armature  and  Field  Strength. — Since  the  torque 
of  a  motor  depends  on  the  product  of  field  flux  and  armature 
current,  a  change  in  the  flux  will 
cause  a  proportional  variation  in 
the  torque  for  a  constant  value 
of  armature  current.  Likewise, 
since  the  speed  depends  directly 
on  the  counter  e.m.f.  and  in- 
versely on  the  field  flux,  a  change 
in  flux  at  any  value  of  armature 
current  will  cause  an  inverse 
effect  on  the  speed.  In  the 
shunt  motor  the  field  strength 
may  be  readily  varied  by  insert- 
ing resistance  in  series  with  the 
field  windings;  but  in  the  series 
motor  it  is  less  easy  to  make  the 

TViprp  nrp  frmr  mpthnrk       ,    This    method    of    field    weakening    has 
^ie  are  lOUr  IlietllUUb       been  abandoned  on  account  of  inductive 


Resistance 


FIG.  42. — Field  weakening  by 
diverting  resistor. 


which  may  be  employed  to  vary 

the  field  strength  in  series  motors,  as  follows: 

1.  Placing  resistance  in  parallel  with  the  field  winding. 

2.  Short-circuiting  portions  of  the  field  winding. 

3.  Cutting  out  of  circuit  portions  of  the  field  winding. 

4.  Placing  halves  of  the  field  coils  in  series  and  in  parallel. 

Of  these  methods,  the  first,  shown  diagrammatically  in  Fig.  42, 
was  used  in  the  early  days  of  electric  railways.  It  was  soon 
abandoned  on  account  of  the  severe  sparking  occasioned  with 
the  weakened  field.  In  the  motors  of  that  period  the  problem 
of  commutation  was  not  understood  so  well  as  it  is  at  the  present 
time,  and  the  margin  of  field  strength  was  not  great  enough  to 
permit  this  practice.  With  modern  motors,  equipped  with 
interpoles,  the  commutation  is  so  much  better  that  a  certain 
amount  of  field  weakening  is  permissible  without  any  trouble 


88 


THE  ELECTRIC  RAILWAY 


from  sparking.  Further,  in  the  designs  arranged  for  this  method 
of  control,  the  flux  with  the  full  field  in  circuit  is  considerably 
greater  than  for  the  ordinary  motor  not  arranged  for  field 
weakening. 

The  use  of  a  resistance  in  parallel  with  the  field  is,  however, 
open  to  several  objections.  It  places  a  non-inductive  path  for 
the  current  in  parallel  with  a  highly  inductive  one.  If  the  load 
is  suddenly  varied,  the  resulting  change  in  current  will  at  first 
be  practically  all  made  through  the  resistance,  on  account  of  the 
inductive  effect  of  the  field  winding.  The  current  will  after- 
ward gradually  build  up  in  the  field  coils;  but  sometimes  not 


FIG.  43. — Field  weakening  by  short- 
circuiting  turns. 


Field 


FIG.  44. — Field  weakening  by 
cutting  out  turns. 

This  method  and  that  shown  in  Fig.  43 
are  in  general  use  where  field  control 
motors  are  employed.  The  reduction  in 
the  number  of  turns  is  usually  from  20  to 
30  per  cent. 


until  considerable  damage  has  been  done  due  to  sparking  or 
flashing  at  the  commutator  under  the  abnormal  conditions. 

The  second  method  is  to  be  preferred  to  the  first.  In  this,  as 
shown  in  Fig.  43,  all  the  current  must  pass  through  the  field 
winding,  no  matter  what  momentary  variations  in  current  strength 
there  may  be.  This  is  a  marked  advantage  over  the  use  of  par- 
allel resistance. 

The  third  method,  illustrated  in  Fig.  44,  is  electrically  the  same 
as  the  second,  and  gives  precisely  the  same  results.  The  only 
difference  is  that  the  portion  of  the  winding  not  in  use  is  entirely 
cut  out,  instead  of  being  merely  short-circuited. 


CONTROL  OF  RAILWAY  MOTORS 


89 


In  the  fourth  method,  Fig.  45,  the  turns  which  are  removed 
from  the  circuit  in  the  second  and  third  methods,  are  connected 
in  parallel  with  the  other  portion  of  the  winding.  This  arrange- 
ment will  only  allow  of  two  combinations,  with  full  and  half 
ampere  turns.  It  has  the  advantage  over  the  second  and  third 
methods  of  loading  all  parts  of  the  field  winding  equally. 

The  efficiencies  of  the  first  three  connections  are  identical,  if 
the  amount  of  field  weakening  is  the  same.  Consider  the  field 
strength  reduced  to  one-half  its  normal 
value  by  each  method.  In  the  first  this 
will  be  accomplished  by  placing  a  resistor 
in  parallel  with  the  field  whose  resistance 
is  equal  to  that  of  the  field  winding.  The 
total  resistance  of  the  combination  is  one- 
half  that  of  the  field  alone,  and  the  am- 
pere turns  in  the  field  coils  one-half  the 
normal  value  for  the  same  armature  cur- 
rent. With  the  second  or  third  methods 
of  connection,  the  resistance  is  reduced  to 
one-half  the  normal  value,  since  one-half  of 
the  winding  is  removed  from  the  circuit. 
The  efficiency  of  either  connection  is,  there- 
fore, the  same  as  for  the  first.  In  the 
fourth  connection  it  is  greater,  since,  when 
the  two  halves  of  the  field  are  connected  in 
parallel,  the  resistance  of  the  combination  is 
but  one-quarter  the  normal  value.  In  any  of  the  four  methods  of 
connection,  the  ampere  turns  on  the  field  will  be  the  same,  if  the 
parallel  resistance  is  equal  to  that  of  the  field,  if  one-half  of  the 
field  turns  are  short-circuited  or  cut  out  of  the  circuit,  or  if  the 
halves  of  the  winding  are  connected  in  parallel  instead  of  in  series. 
The  one  to  be  used  in  any  particular  case  depends  on  the  size  of 
the  motor  and  the  conditions  of  operation.  For  small  machines, 
either  the  second  or  third  method  of  connection  may  be  used  to 
advantage.  For  large  locomotive  motors,  the  additional  com- 
plication of  the  winding  and  connections  in  the  fourth  method  is 
warranted  on  account  of  the  lower  loss  and  the  smaller  heating. 

Changes  in  Number  of  Poles,  and  in  Frequency. — These 
methods  of  control  are  only  applicable  to  induction  motors. 
They  will  be  considered  in  detail  in  connection  with  the  con- 
trol of  motors  of  this  type. 


FIG.  45.  — Field 

3akening  tn 
fields  in  para! 


weakening  by  placing 


This  method  is  usually 
applicable  only  to  the 
larger  locomotive  motors. 


90  THE  ELECTRIC  RAILWAY 

Practical  Combinations  of  Control  Methods. — In  the  practical 
control  of  railway  motors,  one  or  more  of  the  methods  outlined  in 
the  preceding"  paragraphs  may  be  used  to  give  the  proper  varia- 
tion in  characteristics  desired.  The  simplest  method  is  to  con- 
trol the  potential;  for  alternating  current  this  may  be  readily 
done  with  the  aid  of  a  transformer.  For  direct  current,  no  simple, 
and  at  the  same  time  efficient,  method  is  available.  For  small 
equipments,  or  those  which  are  infrequently  started,  the  plain 
rheostatic  method  is  the  simplest  and  most  rugged  combination 
that  can  be  used.  The  chief  disadvantage  lies  in  the  waste  of 
energy  in  the  resistors.  The  method  in  most  general  use  is  a 
combination  of  the  rheostatic  control  with  changes  in  arrange- 
ment of  the  motors,  placing  them  in  series  and  in  parallel.  Since 
there  are  several  methods  of  accomplishing  the  results  sought, 
they  will  be  taken  up  more  in  detail  in  the  succeeding  paragraphs. 

Rheostatic  Control. — The  simplest  way  of  controlling  the  per- 
formance of  one  or  more  series  motors  is  by  the  rheostatic  method. 
Resistance  is  placed  in  series  with  the  motor  or  motors,  the  value 
being  determined  by  the  current  desired  through  the  motor  at 
starting.  Taps  are  taken  from  the  resistors  at  certain  points, 
so  that  the  resistance  may  be  varied  from  the  maximum  value  to 
zero  in  a  fixed  number  of  steps.  The  proportioning  of  the  resis- 
tance values  is  done  in  the  same  way  as  for  series-parallel  control- 
lers, and  may  be  determined  as  in  the  example  under  that 
heading.  It  must  be  remembered  that  since  there  is  usually 
only  one  motor,  the  full  line  potential  will  be  impressed  on  the 
motor  circuit  at  the  start,  and  the  values  of  resistance  must 
be  determined  accordingly. 

A  number  of  practical  controllers  have  been  designed  using  the 
rheostatic  principle.  All  of  the  early  ones  were  of  this  type,  the 
series-parallel  connection  not  being  widely  adopted  at  first.  The 
best  known  modern  controllers  of  this  kind  are  the  Type  R,  which 
are  sold  by  the  leading  electrical  manufacturers  in  this  country. 
A  number  of  sizes  are  built,  the  main  difference  being  in  the 
capacity  of  the  motors  which  can  be  handled.  A  controller  of  this 
type  consists  essentially  of  a  rotatable  drum  carrying  a  number  of 
copper  segments  arranged  to  make  the  proper  sequence  of  con- 
nections. A  set  of  fingers,  connected  to  the  various  external 
circuits,  are  brought  to  bear  on  the  segments  as  the  drum  is 
revolved  beneath  them. 


CONTROL  OF  RAILWAY  MOTORS 


91 


The  development  of  a  rheostatic  controller,  known  as  the  type 
R-17,  is  shown  in  Fig.  46.  This  controller  is  suited  for  use  with 
one  40  kw.  motor.  The  operation  may  be  readily  traced  from  the 
diagram,  the  maximum  resistance  being  connected  in  series  on  the 
first  point  and  cut  out  in  steps  until  the  motor  is  working  on  the 
full  line  potential.  With  this  type  of  controller,  as  with  any 
rheostatic  control,  there  is  but  one  running  point,  that  where  the 
motor  is  connected  directly  to  the  line.  On  that  point  all  the 
resistance  is  short-circuited,  and  the  loss  in  the  controller  is  simply 
that  of  any  closed  switch. 


(Qroundedj 


FIG.  46. — Development  of  type  R  controller. 

This  form  of  controller  is  used  principally  for  the  control  of  single  motors  for  mining  and 
industrial  work.  It  is  seldom  employed  for  railway  cars. 

Rheostatic  controllers  are  also  made  for  operation  with  sev- 
eral motors,  permanently  connected  in  series  or  in  parallel;  and 
in  some  others  of  this  type,  provision  is  made  for  connecting  motors 
in  series  or  in  parallel  by  means  of  a  commutating  switch  located 
in  the  same  case,  and  sometimes  on  the  same  shaft  with  the 
reversing  drum. 

Limitations  of  Rheostatic  Control. — Controllers  of  the  rheo- 
static type,  while  they  are  of  the  greatest  simplicity,  and  are 
extremely  rugged,  are  limited  in  their  present  application  almost 
entirely  to  mining  locomotives.  Practically  none  are  used  on 
electric  railways  of  any  description,  having  been  superseded 
entirely  by  series-parallel  controllers.  The  reason  for  this  is 


92 


THE  ELECTRIC  RAILWAY 


found  in  their  low  efficiency  of  operation.  During  the  period 
while  resistance  is  connected  in  series  with  a  motor  or  a  set  of 
motors,  a  portion  of  the  electrical  input  is  being  consumed  in  the 


800   400  40 


600  300  30 


45 


Time,  Seconds. 


FIG.  47. — Energy  loss  with  rheostatic  control. 

The  shaded  area  represents  the  energy  wasted  in  resistance.     It  is  nearly  one-half  of  the 
entire  input  while  the  controller  is  being  turned  to  the  full-on  position. 


800    400  40 


45 


FIG.  48. — Energy  loss  with  series-parallel  control. 

In  this  control  the  wasted  energy  is  but  one-half  as  great  as  in  the  rheostatio  control. 
Approximately  one-fourth  the  input  shown  in  Fig.  47  has  been  saved. 

resistors.  The  input  to  the  motors  is  therefore  less  than  the 
input  to  the  train  by  the  amount  consumed  in  the  wiring  and  in 
the  resistors.  For  short  runs  this  may  amount  to  a  very  consid- 
erable part  of  the  total  input  if  rheostatic  controllers  are  used. 


CONTROL  OF  RAILWAY  MOTORS 


93 


In  Fig.  47  is  shown  a  curve  between  power  input  and  time  for  a 
certain  run,  using  four  motors  in  parallel  with  rheostatic  control. 
The  shaded  area  is  a  measure  of  the  energy  used  in  the  resistors. 
This  shaded  portion  represents  approximately  one-half  the  total 
input  during  the  period  while  the  controller  is  being  turned  to  the 
full-speed  position. 

The  same  motors  may  be  connected  in  groups  of  two  in  parallel, 
and  operated  with  a  series-parallel  control  to  give  the  same 
acceleration.  In  Fig.  48  is  shown  the  curve  of  input  for  this  form 
of  control.  The  shaded  area,  representing  the  loss,  is  only  one- 


800  400  40 


600  300   30  — 


400   200   ZO  - 


200    100    10  * 


I 
< 

t" 


FIG.  49. — Energy  loss  with  series,  series-parallel  control. 

The  energy  saving  over  the  series-parallel  control  is  much  less  than  that  of  the  latter  over 
the  rheostatic.  For  this  reason  it  has  not  a  very  wide  application  for  light  railway  service. 

half  as  large  as  in  Fig.  47.  This  saving  amounts  to  one-fourth  of 
the  total  energy  input  during  the  time  of  operating  the  controller, 
and  is  a  considerable  portion  of  the  entire  input  for  the  run. 

Following  the  same  line  of  argument,  it  may  be  seen  that  a 
controller  can  be  arranged  to  put  all  four  motors  in  series,  re-con- 
nect them  in  series-parallel  at  the  proper  time,  and  finally  place 
them  in  full  parallel.  The  power  curve  for  such  a  control  is 
shown  in  Fig.  49.  It  may  be  noted  that  the  saving  in  energy 
is  about  one-half  of  that  lost  in  the  series  connection  of  the  single 
series-parallel  control,  and  one-eighth  of  the  loss  by  the  rheostatic 
method.  It  is  only  one-sixteenth  of  the  input  during  the  ac- 
celeration period,  and  a  much  smaller  portion  of  the  entire 
energy  input  for  the  run.  While  any  saving  of  energy  is  a  good 


94  THE  ELECTRIC  RAILWAY 

thing,  the  resulting  complication  of  the  controller  is  so  great  that 
it  usually  overbalances  the  gain.  The  saving  incident  to  the 
series-parallel  over  the  rheostatic  control  is  so  much  larger  that 
the  complication  is  thereby  justified. 

Another  advantage  may  be  gained  by  the  use  of  series-parallel 
control.  With  the  rheostatic  method,  there  is  only  one  efficient 
operating  point,  that  being  the  position  with  all  resistance  cut 
out  of  circuit.  For  reduced  speeds  it  is  necessary  to  waste  a 
large  amount  of  the  input  in  the  resistors.  By  the  use  of  single 
series-parallel  control,  a  second  efficient  operating  speed  becomes 
available  when  the  motors  are  connected  in  series.  The  efficiency 
of  the  motors  on  half-potential  is  slightly  less  than  under  normal 
conditions,  but  it  is  quite  high  compared  with  the  efficiency  when 
half-speed  is  obtained  by  rheostatic  control.  Even  without  the 
saving  in  energy  during  acceleration,  the  complication  of  the  con- 
trol is  justified  to  obtain  the  second  operating  point,  which  gives 
approximately  half  the  full  speed. 

By  the  use  of  the  series,  series-parallel  control,  an  additional 
operating  speed  of  about  one-fourth  the  normal  may  be  obtained. 
This  is  not  needed  in  ordinary  car  operation;  but  in  the  case  of 
locomotives  which  must  do  a  certain  amount  of  switching  and 
slow-speed  yard  work,  the  extra  efficient  speed  will  justify  the 
added  complication.  It  is  only  used  on  a  few  of  the  larger  loco- 
motives which  are  designed  for  normal  high  speeds.  Generally 
speaking,  all  of  the  controllers  for  direct-current  series  motors  are 
of  the  single  series-parallel  type,  either  with  two-motor  or  four- 
motor  equipments. 

Series -Parallel  Control. — Practically  all  direct-current  railway 
motor  equipments  consist  of  two,  or  multiples  of  two,  series 
motors,  controlled  by  the  series-parallel  method.  The  basic 
principle  of  this  control  is,  as  has  already  been  stated,  to  first  put 
the  two  motors  in  series  with  resistance,  next  to  cut  it  out  of  the 
circuit  in  a  few  steps,  then  to  change  the  connections  to  parallel 
with  a  certain  amount  of  resistance,  and  finally  to  cut  it  out  again 
in  steps.  In  some  types  of  series-parallel  control,  the  additional 
feature  is  included  of  reducing  the  field  turns  on  the  parallel  con- 
nection after  the  external  resistance  is  short-circuited. 

The  main  differences  in  the  arrangements  of  series-parallel 
controllers  are  occasioned  by  the  methods  of  changing  from  the 
series  to  the  parallel  connection.  It  may  be  easily  seen  that  the 
change  from  series  to  parallel  can  be  made  by  one  of  two  methods 


CONTROL  OF  RAILWAY  MOTORS 


95 


— to  open  the  motor  circuits  entirely  while  re-connecting,  or  to 
short-circuit  one  of  the  motors.  Small  platform  or  "hand" 
controllers  are  usually  of  the  latter  type,  and  are  made  in  various 
sizes,  as  required  by  equipments  of  different  capacity. 

Type  K  Controllers. — The  best  known  series-parallel  control- 
lers in  America  are  the  "Type  K."  This  type  (see  Fig.  50, 
which  represents  the  K-ll  controller)  consists  of  a  drum  carrying 
a  number  of  copper  segments,  the  connections  to  the  circuits 
being  made  through  corresponding  stationary  fingers  which  press 
against  the  segments  as  the  drum 
is  rotated  beneath  them.  The 
general  arrangement  is  quite  simi- 
lar to  that  of  the  Type  R  rheo- 
static  control  lers.  The  small 
drum  at  the  right  is  for  the  pur- 
pose of  reversing  the  direction  of 
rotation  of  the  motors,  this  being 
accomplished  by  interchanging 
either  the  field  or  the  armature 
connections.  To  prevent  the  de- 
struction of  the  segments  and 
fingers  by  arcing  when  breaking 
the  circuits,  the  well-known  action 
of  the  magnetic  field  on  an  arc  is 
employed  in  the  so-called  "mag- 
netic blow-out."  A  coil  carrying 
the  main  motor  current  is  wound 
on  an  iron  core  fastened  to  the 
cast-iron  back  of  the  controller  case,  which  thus  becomes  one 
pole  of  an  electromagnet.  The  other  pole  is  of  such  a  shape  that 
the  flux  produced  must  pass  across  the  places  where  arcing  will 
occur,  and  tend  to  break  the  arc  before  it  has  damaged  the  con- 
tacts. Since  the  front  cover  of  the  controller  is  of  sheet  iron,  a 
certain  amount  of  flux  passes  through  it  instead  of  across  the 
contacts,  reducing  the  efficiency  of  the  magnetic  blow-out  by  as 
much  as  one-half. 

The  contacts  on  the  reverse  drum  are  not  made  sufficiently 
heavy  to  stand  arcing,  and  they  are  not  protected  by  a  magnetic 
blow-out.  It  is  hence  necessary  to  prevent  the  reverse  drum 
being  thrown  while  current  is  passing  through  the  contacts. 
This  is  accomplished  by  interlocking  the  two  drums  together 


FIG.  50.— Type  K-ll  controller. 

The  type  K  controllers  are  very  widely 
used  in  America  for  the  control  of  fairly 
small  motors  by  the  series-parallel 
method.  Practically  all  street  cars  use 
this  form  of  controller. 


90 


THE  ELECTRIC  RAILWAY 


by  a  dog,  which  prevents  motion  of  the  reverse  lever 
except  when  the  main  controller  handle  is  in  the  "off"  position. 
Since  it  is  inadvisable  for  the  motorman  to  leave  his  car  in  such 
condition  that  there  is  any  possibility  of  irresponsible  persons 
operating  the  controller,  an  interlock  is  arranged  so  that  the 
reverse  lever  cannot  be  removed  except  when  the  drum  is  in  the 
"off"  position,  i.e.,  midway  between  the  "forward"  and  "re- 
verse" positions.  When  the  reverse  lever  is  removed,  another 
interlock  will  prevent  the  rotation  of  the  main  drum;  hence  the 


I    2 


FIG.  51 — Development  of  Type  K-10  controller. 

The  Type  K  controllers  are  made  in  a  number  of  different  models.  The  one  shown  is 
suitable  for  the  control  of  two  series  motors.  The  difference  is  principally  in  the  number 
of  resistance  steps,  and  in  the  number  of  motors  which  may  be  connected  to  the  reverse 
drum. 

reverse  drum  cannot  be  improperly  operated  under  any  condi- 
tions that  may  arise. 

In  case  of  emergencies  it  may  be  necessary  to  operate  the  car 
with  only  one  motor  or  pair  of  motors.  Switches  are  provided 
(near  the  base  of  the  controller)  to  cut  out  of  the  circuit  either  one. 
When  one  of  the  motors  is  out  of  the  circuit,  there  is  no  object  in 
turning  the  controller  drum  beyond  full  series,  since  that  position 
will  place  the  motor  on  the  line  without  resistance.  The  switches 
for  cutting  out  the  motors  are  provided  with  interlocks  preventing 


CONTROL  OF  RAILWAY  MOTORS  97 

the  drum  from  being  turned  beyond  the  last  series  notch  when 
either  switch  is  closed. 

A  development  of  the  K-10  controller  is  shown  in  Fig.  51. 
From  this  diagram  the  sequence  of  connections  may  be  clearly 
traced.  The  points  which  are  suitable  for  continuous  operation 
are  designated  as  "  running  points."  It  is  obvious  that  it  would  be 
unwise  to  operate  continuously  with  external  resistance  in  the  cir- 
cuit on  account  of  the  reduction  in  efficiency.  Moreover,  the 
resistors  are  not  designed  to  carry  the  motor  current  for  more 
than  a  few  minutes  without  overheating. 

When  it  is  desired  to  use  a  controller  of  this  type  with  an 
equipment  of  four  motors,  the  main  drum  is  exactly  similar  to 
that  of  a  two-motor  controller.  The  motors  are  permanently  ar- 
ranged in  groups  of  two ;  and  the  only  difference  in  the  controller 
is  the  extension  of  the  reverse  drum  to  provide  additional  con- 
tacts for  the  field  and  armature  circuits  of  the  four  motors.  Gen- 
erally, the  two  machines  of  a  group  are  placed  in  parallel;  but  if 
the  equipment  consists  of  four  600-volt  motors  to  be  operated  on  a 
1200-volt  circuit,  the  pairs  will  be  arranged  in  series.  On  some 
roads,  where  a  portion  of  the  line  is  at  1200  volts  and  another 
portion  at  600  volts,  the  motor  connections  may  be  changed  by 
an  independent  switch,  which  is  interlocked  with  the  controller 
to  prevent  improper  operation. 

Type  L  Controller. — The  "Type  L"  controller,  which  was 
formerly  much  used  for  the  heavier  equipments,  is  similar  in  its 
general  mechanical  design  to  the  Type  K.  The  main  difference  is 
in  the  method  of  changing  from  the  series  to  the  parallel  connec- 
tion, which  is  accomplished  by  opening  the  motor  circuits  while 
making  the  change,  as  shown  in  Fig.  52.  This  type  of  controller 
has  been  practically  superseded  by  various  forms  of  so-called 
"multiple-unit"  control. 

A  few  years  ago,  considerable  trouble  was  experienced  on  ac- 
count of  controllers  being  used  for' handling  heavier  currents  than 
they  were  designed  for.  This  sometimes  resulted  in  the  contacts 
being  completely  burned  out,  or  at  least  rendered  useless  tempo- 
rarily. This  became  so  serious  that  the  leading  manufacturers 
have  placed  on  the  market  an  improvement  in  providing  an  auto- 
matic switch  for  closing  and  opening  the  main  circuit  so  that 
the  controller  drum  is  relieved  of  this  duty.  This  switch  is 
operated  electrically  from  the  main  controller,  but  is  mechanic- 
ally independent  of  it,  usually  being  placed  beneath  the  car. 


98  THE  ELECTRIC  RAILWAY 

Some  of  the  ordinary  types  of  platform  controller  have  been 
modified  by  being  provided  with  an  auxiliary  trip  on  the  main 
drum,  which  prevents  the  contactor  from  closing  until  the  operat- 
ing handle  has  been  turned  to  the  first  notch,  after  which  the 
circuit  operating  the  switch  is  closed.  This  prevents  burning  of 
the  fingers  on  closing  the  main  circuit.  When  the  drum  is  turned 
backward  to  cut  off  the  current,  the  operating  circuit  is  opened 
before  the  drum  has  been  returned  to  the  off  position,  so  that  in 
this  case  the  arc  is  also  taken  by  the  contactor.  This  system  may 
be  further  developed  by  using  the  switch  under  the  car  as  an 
auxiliary  circuit  breaker,  whose  tripping  coil  is  in  the  trolley  cir- 
cuit, and  whose  jaws  are  in  the  operating  circuit  of  the  contactor. 

Series  Parallel 


r-VWWVi 
•\y^ 

LA/VWW 


Full 
Parallel 


''•Circuif  Open-1 
FIG.  52.  —  Circuits  of  Type  L  Controller. 

This  controller  was  formerly  much  used  for  large  equipments,  but  has  now  been  superseded 
by  the  various  forms  of  multiple-unit  control,  as  shown  in  Figs.  53  and  54. 

It  can  be  set  to  open  at  any  desired  value  of  current  within  its 
operating  limits.  When  the  current  reaches  this  value,  the 
tripping  coil  breaks  the  operating  circuit,  thus  opening  the  main 
contacts. 

Multiple-Unit  Control.  —  When  it  is  desired  to  operate  a  number 
of  cars  in  a  train,  there  are  two  general  methods  of  procedure. 
The  cars  may  be  left  without  electrical  equipment,  and  the  power 
concentrated  in  a  locomotive;  or  each  car,  or  as  many  of  them  as 
required,  may  be  equipped  with  electric  motors  and  controllers. 
There  are  many  arguments  against  the  use  of  locomotives  in  this 
type  of  service,  and  in  general  the  use  of  motor  cars  is  preferred. 
The  successful  operation  of  a  train  of  motor  cars  depends  to  a 
great  extent  on  having  the  motors  divide  the  work  equally. 


CONTROL  OF  RAILWAY  MOTORS  99 

To  do  this  the  controllers  must  all  be  moved  at  the  same  rate. 
This  cannot  be  done  satisfactorily  by  having  a  motorman  on  each 
car,  since  it  is  practically  out  of  the  question  to  have  them  syn- 
chronize their  movements.  Further,  this  would  increase  the  cost 
of  platform  labor  to  a  prohibitive  amount. 

The  ideal  system  is  one  in  which  all  the  motor  cars  are  controlled 
by  one  motorman,  who  can  be  located  at  any  convenient  position 
on  the  train,  as  at  the  front  of  the  leading  car,  whether  that  be  a 
motor  car  or  a  trailer.  In  addition,  it  is  desirable  to  be  able  to 
change  the  number  of  cars  in  a  train  at  will,  depending  on  the 
amount  of  traffic.  All  these  advantages  may  be  obtained  with 
any  one  of  the  forms  of  multiple-unit  control  now  in  use  on  the 
large  electric  roads  in  all  parts  of  the  country. 

Sprague  System. — The  earliest  method  of  control  of  the  multi- 
ple-unit type  Was  the  Sprague  system,  invented  by  Lieut.  Frank 
J.  Sprague,  and  first  used  on  the  South  Side  Elevated  Railway  in 
Chicago.  In  this  system  the  main  or  motor  controller  was  a  drum 
similar  to  that  of  the  Type  K  platform  controller,  but  differing 
from  it  in  being  operated  by  a  " pilot  motor."  This  latter  was 
under  the  control  of  the  motorman,  who  could  cause  its  armature 
to  rotate,  thus  revolving  the  main  control  cylinder  and  making 
the  proper  connections  for  the  acceleration  of  the  car  motors. 
A  number  of  novel  devices  were  incorporated  in  this  type  of 
control.  In  order  to  start  the  car,  all  that  was  necessary  was 
for  the  motorman  to  start  the  pilot  motor  in  operation,  which 
would  begin  the  revolution  of  the  main  controller  drum.  The 
rate  of  movement  of  this  drum  was  limited  by  the  propulsion  cur- 
rent. A  relay  was  interposed  in  the  main  control  circuit,  and  so 
arranged  that  if  the  live  current  exceeded  a  predetermined 
amount,  the  circuit  of  the  pilot  motor  would  be  broken,  stopping 
the  movement  of  the  main  drum  until  the  live  current  fell  below 
the  limiting  value.  Then  the  pilot  motor  would  again  be  con- 
nected to  its  circuit  and  the  cylinder  be  revolved  further.  This 
action  would  continue  until  the  propulsion  motors  were  in  the  full 
parallel  connection.  A  number  of  other  relays  were  introduced 
to  make  the  operation  more  certain,  and  to  prevent  abuse  of  the 
equipment.  Magnetic  blow-outs  similar  to  those  used  on  the 
platform  controllers  were  employed.  In  general,  its  operation 
was  quite  satisfactory  for  fairly  small  cars,  taking  not  over  about 
150  kw.  total  capacity. 


100 


THE  ELECTRIC  RAILWAY 


Type  M  Control. — When  the  original  Sprague  controller  was 
used  for  heavy  equipments  it  was  found  inadequate;  so  when 
the  Sprague  patents  were  purchased  by  the  General  Electric 
Company  the  manufacture  of  the  original  Sprague  control  was 
abandoned,  the  "Type  M"  control  being  substituted  for  it. 
This  latter,  shown  diagram  mat  ically  in  Fig.  53,  utilizes  the  princi- 
ple mentioned  in  connection  with  the  heavy  Type  K  controllers 
of  breaking  the  circuit  in  specially  designed  contactors.  A  set 
of  magnetically  operated  switches  is  substituted  for  the  drum. 


FIG.  53. — Circuits  of  type  M  controller. 

This  type  of  controller  is  very  widely  used  on  elevated  and  interurban  cars.      Motors  of 
practically  any  capacity  may  be  handled. 

These  are  actuated  by  a  small  current  from  the  trolley,  and  their 
movement  is  governed  by  the  motorman  through  a  "  master 
controller,"  whose  function  is  to  admit  current  to  the  proper 
switches  and  secure  the  correct  sequence  of  closing  and  opening 
them  to  obtain  the  desired  combinations.  The  location  of  the 
master  controller  may  thus  be  practically  independent  of  the 
main  controller,  the  only  connection  being  through  the  small 
wires  for  supplying  current  to  the  magnets  for  operating  the  main 
switches  of  the  control.  Two  types  of  operation  are  standard: 
that  providing  manual  control  of  the  switches,  and  that  in  which 


CONTROL  OF  RAILWAY  MOTORS  101 

the  movement  of  the  switches  is  automatically  governed  by 
the  motor  current,  as  in  the  original  Sprague  system. 

The  essential  element  of  the  system,  the  "unit  switch"  or 
"  contactor,"  is  a  switch  actuated  by  an  electromagnet.  Each  of 
these  units  may  be  considered  as  replacing  a  finger  and  its  corre- 
sponding segment  in  the  hand-operated  controllers,  and  consists 
of  a  pair  of  contacts,  one  of  which  is  fixed,  and  the  other  moved  by 
the  action  of  the  solenoid.  The  pair  of  contacts  operate  in  an  arc 
chute  of  moulded  insulation  with  an  individual  magnetic  blow- 
out. To  insure  the  proper  sequence  of  closing  and  opening  the 
switches,  interlocks  are  provided  for  making  the  necessary  con- 
nections. All  of  the  contactors  are  placed  in  a  covered  metal  box 
mounted  on  an  insulated  support  beneath  the  car,  or  in  the  cab 
of  the  locomotive.  Since  each  contactor  is  independent  of  the 
others,  the  capacity  of  the  switch  may  be  made  as  large  as  required 
for  the  particular  case.  The  size  of  motors  which  can  be  handled 
is  not  limited,  as  with  the  drum  type  of  controller.  In  case  the 
desired  capacity  is  too  great  for  a  single  switch,  two  or  more  may 
be  placed  in  parallel  to  subdivide  the  current. 

The  automatic  control  provides  for  the  acceleration  of  the  train 
at  a  predetermined  value  of  motor  current,  although  it  does  not 
prevent  manual  operation  of  the  controller  at  a  lower  rate  if  de- 
sired. The  arrangement  is  quite  similar  to  that  described  for  the 
original  Sprague  control.  The  operation  of  the  contactors  is 
governed  by  a  limit  switch  in  the  motor  circuit,  so  that  the  motor 
current  while  accelerating  is  confined  within  a  definite  range. 
This  is  accomplished  by  having  interlocking  contacts  on  certain 
of  the  switches,  the  movement  of  each  connecting  the  magnet 
coil  of  the  next  succeeding  contactor  to  the  control  circuit. 
Under  all  conditions  the  contactors  are  energized  in  a  definite 
order,  as  described  in  the  general  paragraph  on  the  series-parallel 
controller.  The  progression  of  switches  can  be  arrested  at  any 
point  by  the  master  controller,  and  is  also  governed  by  the  limit 
switch,  so  that  the  rate  of  movement  is  never  beyond  that  which 
will  keep  the  motor  current  within  the  prescribed  range. 

Unit  Switch  Control. — The  system  used  by  the  Westinghouse 
Company  is  quite  similar  to  that  just  described,  differing  mainly 
in  the  means  used  to  operate  the  individual  "unit  switches" 
or  contactors.  While  in  the  Type  M  system  the  switches  are 
operated  electrically  by  means  of  current  taken  from  the  line,  in 
the  Westinghouse  control  they  are  actuated  by  means  of  com- 


102 


THE  ELECTRIC  RAILWAY 


pressed  air  supplied  from  the  air-brake  reservoirs.  The  admission 
of  air  to  the  operating  cylinders  is  controlled  by  electrically  oper- 
ated needle  valves.  The  current  for  them  may  be  obtained 
either  from  a  low-potential  storage  battery  or  from  the  line.  The 
main  claims  in  favor  of  this  type  of  control  are  that  a  more 
positive  action  of  the  switches  may  be  obtained  on  account  of  the 
greater  pressures  possible  between  the  contact  fingers.  The 
general  features  of  operation  are  quite  similar  to  those  of  the  Type 
M  control;  in  fact,  both  equipments  may  be  arranged  to  be  oper- 


Master  Controller 

Grounded  on  frame 


B.O. 


( Cutout  Snitches  a,b&.c  are 
\  Connected  to  No.  I  Handle 
\  Cutout  Switches  dc,&fare 
Connected  fo  No.  ?  Handle 


Sequence  of  Switches 


LS 

Q 

P 

Ei 

1 

U 

0 

a 

<J 

O 

3 

U 

U 

o 

4 

U 

O 

o 

5 

o 

o 

o 

o 

() 

O 

0 

o 

6 

0 

(_) 

u 

u 

o 

7 

(     ) 

(.  ) 

u 

o 

6 

Q 

<J 

U 

u 

u 

o 

9 

U 

Q 

u 

Q 

g 

Q_ 

Switch  Group 
FIG.  54. — Circuits  of  type  HL  control. 

In  this  type  of  controller  the  magnetic  switches  of  the  Type  M  controller  are  replaced  with 
electrically  controlled,  pneumatically-operated  switches.  Controllers  of  this  general  type 
are  made  for  a  wide  range  of  equipment. 

ated  together  on  one  train  from  one  master  controller.     Fig.  54 
gives  a  diagram  showing  the  connections  of  this  control. 

Bridge  Connection. — In  some  of  the  types  of  multiple-unit  con- 
trol, as  well  as  in  some  of  the  later  Type  K  controllers  of  large 
size,  the  change  from  series  to  parallel  is  made  without  either 
short-circuiting  or  open-circuiting  the  motors.  This  is  accom- 
plished by  the  " bridge"  connection.  It  consists  in  putting  a 
resistance  in  parallel  with  the  motors,  and  through  it  making  the 
change.  This  is  shown  in  Fig.  55.  The  principle  of  the  bridge 


CONTROL  OF  RAILWAY  MOTORS  103 

connection  is  to  have  the  resistance  placed  in  parallel  with  the 
motors  such  that  the  current  flowing  through  it  is  practically  the 
same  as  the  motor  current.  Then  when  the  connections  are 
changed  to  parallel,  there  will  be  no  disturbance  in  the  total  current 
taken  by  either  motor  or  by  the  line.  The  success  of  this  arrange- 
ment depends  on  having  the  motor  current  at  the  instant  of 
making  the  change  the  same  as  that  through  the  resistance.  For 
this  reason  the  bridge  connection  is  best  suited  to  automatic 
control,  where  the  current  is  limited  by  electrical  relations  only. 


A/W VW  K[>JUUUUL. — ll" 


FIG.  55. — Bridge  method  of  transition. 

This  method  makes  the  change  from  series  to  parallel  without  breaking  the  circuit 
through  either  motor,  and  without  causing  any  great  disturbance  on  the  line.  It  is  widely 
used  in  connection  with  controllers  of  the  multiple-unit  type. 

Pneumatically-Operated  Drum  Control. — The  drum  controller 
is  at  present  the  most  compact  and  the  most  flexible  device  for 
producing  a  number  of  different  combinations  in  electric  circuits, 
and  it  is  still  the  most  suitable  method  of  control  for  small  equip- 
ments. With  remote  operation  of  the  drum,  and  protection 
against  arcing,  it  makes  a  satisfactory  apparatus  for  multiple- 
unit  control.  A  type  of  controller  has  been  developed,  primarily 
for  single-car  service  on  the  New  York  City  railways,  but  which 
is  applicable  for  multiple-unit  operation  of  any  cars  which  are  not 
too  heavy.  Mechanically,  it  consists  of  an  ordinary  drum  con- 
troller, which  is  actuated  by  a  pair  of  compressed-air  cylinders 


104  THE  ELECTRIC  RAILWAY 

arranged  to  turn  the  main  shaft  through  a  rack  and  pinion.  The 
reverse  drum  is  also  moved  by  air  cylinders.  Admission  and  re- 
lease of  air  are  governed  by  magnetically-operated  needle  valves, 
as  in  the  unit  switch  control.  A  current  limit  relay  is  introduced 
in  the  control  circuit  to  keep  the  motor  current  within  a  pre- 
scribed range.  This  device  operates  in  the  same  manner  as  the 
limit  switches  already  described  with  multiple-unit  control.1 

Jones  Type  Control. — A  novel  type  of  series-parallel  control, 
suitable  for  use  with  four-motor  equipments,  has  been  brought 
out  by  Messrs.  P.  N.  Jones  and  J.  W.  Welsh  of  the  Pittsburgh 
Railways  Co.  It  operates  with  a  permanent  series  connection 
between  all  of  the  motors,  and  employs  a  minimum  of  resistance 
for  securing  the  desired  steps.  At  least  three  of  the  motors  are 
in  circuit  at  all  times. 

The  connections  on  the  different  steps  are  shown  in  Fig.  56. 
The  controller  has  seven  points,  of  which  three,  numbered  2,  4 
and  7,  are  operating  positions.  The  current  in  some  of  the  mo- 
tors is  reversed  in  making  the  changes;  but  since  both  armature 
and  field  are  reversed  together,  the  direction  of  motion  is  not 
changed.  The  first  position  places  all  the  motors  in  series  with  a 
suitable  resistance,  which  is  cut  out  on  the  second  point.  One 
motor  is  completely  short-circuited  on  the  third  notch,  after 
which  it  is  connected  to  the  line  through  resistance.  On  the  next 
transition  point  a  second  motor  is  reversed,  thus  placing  it  in  series 
with  the  other  and  the  resistance.  On  the  fourth  notch  the  re- 
sistance is  cut  out,  leaving  the  motors  in  the  series-parallel 
connection.  The  next  transition  point  is  similar  to  the  other 
transition  connections,  except  that  but  three  motors  are  in  circuit. 
The  fifth  and  sixth  positions  are  really  transition  steps;  and  the 
motors  are  placed  in  full  parallel  on  the  seventh  notch.  This  type 
of  control  has  been  employed  with  success  on  the  cars  of  the 
Pittsburgh  Railways,  which  are  equipped '  with  motors  having 
small  diameter  armatures  on  account  of  the  small-sized  wheel. 
It  is  stated  that  the  control  will  work  equally  well  with  stand- 
ard motors.  For  further  details  of  the  apparatus  and  arrange- 
ments of  the  circuits  reference  may  be  made  to  U.  S.  Patent 
No.  1,109,338,  issued  September  1,  1914. 

Proportioning  of  Resistances. — In  any  of  the  methods  so  far 
devised  for  the  control  of  direct-current  series  motors,  it  is  not 

1  For  a  detailed  description  of  this  type  of  control  see  Electric  Journal, 
October,  1913. 


CONTROL  OF  RAILWAY  MOTORS 


105 


sufficient  to  reduce  the  potential  at  the  motor  terminals  by  the 
use  of  different  combinations  of  motors.  To  prevent  an  excessive 
flow  of  current,  and  to  keep  the  torque  within  rather  narrow  lim- 
its, it  is  necessary  to  introduce  a  certain  amount  of  resistance 
into  the  circuit  in  series  with  the  motors.  The  amount  of  this 
resistance  should  be  just  enough  to  reduce  the  starting  current 


tr 


^^r- 

-/4V- 

FIG.  56. — Jones  type  control. 

In  this  control  combination  of  the  motors  are  used  instead  of  the  usual  resistance,  reducing 
the  energy  loss  while  starting,  and  giving  a  greater  number  of  running  points. 

and  the  torque  to  the  desired  limiting  values  allowable  for  the 
equipment.  As  the  motors  gain  speed,  the  amount  of  resistance 
must  be  lessened,  until  it  is  all  removed  from  the  circuit.  This 
may  constitute  the  entire  control,  or  it  may  be  done  in  conjunc- 
tion with  changes  in  the  arrangement  of  the  motors,  such  as 
connections  in  series  and  in  parallel. 


106  THE  ELECTRIC  RAILWAY 

At  standstill,  the  current  flowing  through  the  motors  is  lim- 
ited only  by  the  resistance  of  the  windings  of  the  machines  con- 
nected in  series,  unless  sufficient  external  resistance  be  inserted  to 
cut  the  current  down  to  some  specified  value. 

As  an  example,  take  the  56  kw.  railway  motor,  curves  for  which 
are  shown  in  Fig.  19.  It  is  desired  to  accelerate  a  certain  car  by 
using  a  pair  of  such  motors  with  series-parallel  control  at  such  a 
rate  that  the  current  will  vary  between  the  limits  of  200  amp.  and 
150  amp.  while  resistance  is  included  in  the  circuit.  The  actual 
determination  of  the  limiting  values  of  current  depends  on  the 
weight  of  the  car,  the  desired  acceleration,  and  the  allowable 
load  on  the  motors.  The  difference  between  the  maximum  and 
minimum  values  of  current  is  determined  by  the  number  of  steps 
on  the  controller,  which  in  its  turn  depends  on  the  permissible 
variation  from  the  mean  acceleration. 

At  standstill  the  current  will  have  the  maximum  value,  and  the 
necessary  resistance  to  be  used  will  be  found  by  Ohm's  law: 

7/  =  ' 


where  /'  is  the  maximum  current,  E  is  the  line  e.m.f.,  Ri  the  ex- 
ternal resistance,  and  r  the  motor  resistance.  In  the  example 
cited,  r  =  0.232  ohm,  hence 


200  - 


+  2  X  0.232 


whence  R\  =  2.036  ohms.  This  represents  the  total  resistance 
which  must  be  added  to  the  motor  circuit  to  keep  the  first  rush 
of  current  down  to  the  desired  limit. 

With  current  passing  through  the  motors,  a  torque  will  be  de- 
veloped, which  will  cause  the  car  to  accelerate.  As  the  car  gains 
speed,  the  motors  develop  a  counter  e.m.f.,  the  production  of 
which  causes  a  decrease  in  the  motor  current,  and  hence  in  the 
tractive  effort  and  the  acceleration.  In  order  to  keep  the  trac- 
tive effort  within  the  limits  desired,  the  resistance  should  be  re- 
duced when  the  current  has  fallen  to  the  minimum  value  decided 
on. 

When  the  current  has  fallen  to  some  value  I",  the  counter 
e.m.f.  developed  by  the  two  motors  in  series,  2EC,  will  be 

2EC  =  E  -  I"(Rl  +  2  r)  (2). 


CONTROL  OF  RAILWAY  MOTORS  107 

It  is  then  necessary  to  determine  the  new  value  of  external  re- 
sistance, Rz,  which  will  cause  the  current  through  the  motors  to 
increase  to  the  maximum  value  /'.  The  reduction  in  resistance 
will  be  made  instantaneously,  so  that  there  will  be  no  opportunity 
for  the  speed  to  change  during  the  operation  of  the  controller 
from  one  notch  to  the  next.  If  the  field  flux  remained  constant 
with  variations  in  armature  current,  as  in  a  shunt  motor,  the 
counter  e.m.f.  would  be  the  same  after  the  resistance  had  been 
reduced,  except  for  the  small  change  in  IR  drop  in  the  motor 
windings.  But  with  the  series  motor,  an  increase  in  armature 
current  carries  with  it  a  corresponding  increase  in  field  flux,  so 
that  the  counter  e.m.f.  will  also  be  greater.  In  order  to  find  the 
amount  of  this  rise  in  counter  e.m.f.,  the  saturation  curve  of  the 
motor  may  be  used,  and  the  two  values  of  flux  corresponding  to 
the  currents  /'  and  I"  determined  from  it.  The  ratio  of  increase 
can  also  be  found  from  the  curve  of  torque  per  ampere,  Fig.  22. 

In  obtaining  the  rise  of  counter  e.m.f.  when  the  resistance  is 
reduced  so  that  the  current  increases  from  I"  amp.  to  I'  amp.,  it 
is  only  necessary  to  determine  the  ratio  of  tractive  effort  per  ampere 
for  the  two  values  of  current.  That  is, 


777  T/ 

J-^C\  1 

1? =   TV'  V"/ 

xl/c2  U 

w 

where  Eci  and  Ec2  are  the  counter  e.m.f. 's  at  currents  /'  and  I" 
respectively,  and  D'  and  D"  the  corresponding  tractive  efforts. 
The  value  of  Eei  having  been  found  already  by  equation  (2),  that 
of  Ec2  can  be  determined  from  equation  (3).  The  new  amount  of 
resistance  will  have  to  be  such  as  to  give  the  counter  e.m.f.  Eez 
when  a  current  /'  flows  through  the  circuit,  which  will  satisfy  the 
equation 

i'  =  trf5  (4) 

This  equation  is  similar  in  form  to  equation  (1),  but  takes  ac- 
count of  any  value  of  counter  e.m.f.  which  may  exist  at  the 
moment. 

Applying  these  equations  to  the  example  cited,  we  have,  from 
equation  (2), 

2Ecl  =  500  -  150  (2.036  +  2  X  0.232)  =  125  volts 


108  THE  ELECTRIC  RAILWAY 

This  is  the  counter  e.m.f  .  existing  the  instant  before  the  resistance 
is  reduced.     The  instant  following  the  reduction,  this  becomes 

1O    A  Q 

2EC2  =  125  X  J^Q  =  135  volts 

The  necessary  value  of  resistance  is  determined  from  the  relation 

500  ~  135 
R2  +  2  X  0.232 

from  which  R2  is  found  to  be  1.361  ohms. 

The  same  reduction  in  torque  as  the  speed  of  the  motor  in- 
creases will  be  noted,  and,  when  the  current  has  fallen  to  150  amp. 
the  counter  e.m.f.  may  be  calculated  by  equation  (2)  as  before. 
A  new  value  of  resistance  may  then  be  found  by  the  use  of  equa- 
tions (3)  and  (4).  This  process  will  be  continued  until  all  the 
resistance  is  cut  out,  and  the  motors  are  connected  in  series  di- 
rectly across  the  line. 

To  obtain  further  acceleration,  it  is  necessary  to  reconnect  the 
motors  in  parallel.  The  counter  e.m.f.  per  motor  will  be  the 
same;  but  when  the  connections  are  changed  to  parallel  the  two 
e.m.f.'s  will  not  add.  Equation  (2)  will  have  to  be  rewritten  as 
follows  : 


Eel  =  #-27"fl  +  (5) 

Having  obtained  the  new  value  for  Eci,  that  of  Ec2  may  be  found 
by  equation  (3).  By  this  method  the  magnitude  of  all  the  par- 
allel resistances  may  be  determined. 

Table  I  shows  these  values  as  computed  for  the  problem  out- 
lined. In  the  columns  for  counter  e.m.f.,  the  upper  values  are 
for  each  motor  (Ec),  and  the  lower  for  the  two  motors  when  they 
are  in  series.  In  the  columns  for  resistance,  the  upper  values  are 
per  motor,  and  the  lower  for  two  motors  in  parallel. 

It  may  be  seen  that  on  points  5  and  9,  on  which  all  resistance 
has  been  cut  out,  the  current  will  not  rise  to  quite  200  amp. 
This  is  unavoidable  with  the  assumptions  made. 

Graphical  Method  of  Calculating  Resistances.  —  This  method 
of  calculation  lends  itself  very  readily  to  a  graphical  solution. 
Referring  to  Fig.  57  a  diagram  has  been  plotted  between  motor 
amperes  and  motor  volts.  If  the  line  e.m.f.  is  500,  then  when  the 
two  motors  are  in  series,  each  will  be  taking  250  volts,  less  what  is 
consumed  in  the  resistance.  The  lines  SE  and  PJ  have  been 


CONTROL  OF  RAILWAY  MOTORS 
TABLE  I 


109 


Point  of 
Controller 

Speed 

Counter  e.m.f. 

IR  Drop 

Resistance 

200  amp. 

150 
amp. 

200  amp. 

150 
amp. 

200 
amp. 

150 
amp. 

Total 

Motor 

External 

1 

0.0 

2.35 

0.0 

62.5 

125.0 

500.0 

375.0 

2.5 

0.464 

2.036 

2 

2.35 

4.26 

67.5 

113.0 

135.0 

226.0 

365.0 

274.0 

1.825 

0.464 

1.361 

3 

4.26 

5.82 

122.2 

154.5 

244.4 

309.0 

255.6 

191.0 

1.278 

0.464 

0.814 

4 

5.82 

7.06 

167.0 

188.5 

334.0 

377.0 

166.0 

123.0 

0.830 

0.464 

0.366 

5 

7.061 

8.09 

203.  61 

215.2 

407.  2] 

430.4 

92.8 

69.6 

0.464 

0.464 

0.0 

6 

8.09 

11.24 

232.0 

299.0 

268.0 

201.0 

1.340 

0.232 

1.108 

0.670 

0.116 

0.554 

7 

11.24 

13.8 

322.5 

366.7 

177.5 

133.3 

0.887 

0.232 

0.655 

0.443 

0.116 

0.327 

8 

13.8 

15.8 

395.0 

421.0 

105.0 

79.0 

0.525 

0.232 

0.293 

0.262 

0.116 

0.146 

9 

15.  S1 

453.  61 

46.4 

0.232 

0.232 

0.0 

drawn  at  an  angle  such  that  the  ordinate,  as  SfEf  or  P'J'  repre- 
sents the  IR  drop  in  one  motor  at  any  current  /.  The  line  SA  has 
been  drawn  to  represent  the  IR  drop  per  motor  for  any  value  of 
current,  when  the  resistance  is  so  chosen  as  to  bring  the  motor  to 
a  standstill  at  200  amp.  When  the  current  has  fallen  to  150 
amp.,  the  total  IR  drop  is  represented  by  the  ordinate  S'A',  and 
the  drop  in  external  resistance  by  E'A'.  If  the  resistance  is  then 
reduced  so  as  to  bring  the  current  to  200  amp.,  the  counter  e.m.f. 
will  be  increased  by  the  ratio  given  in  equation  (5).  The  curve 
TYWT'  between  tractive  effort  per  ampere  and  current  has  been 
plotted  to  the  same  base,  although,  if  the  current  limits  are  to  be 
those  decided  on,  the  points  Y  and  W  are  all  that  need  to  be  lo- 
cated. The  straight  line  WYX  is  then  drawn  through  F  and  W, 
intersecting  the  current  axis  prolonged  at  X.  It  will  be  seen  at 
once,  from  similar  triangles,  that  any  line  drawn  through  X  will 
produce  intersections  on  the  lines  UP'  and  AP"  that  are  propor- 
tional. That  is, 

UA'       UY 

AB  ~  AW 

1  At  196  amperes. 


110 


THE  ELECTRIC  RAILWAY 


and  so  on,  for  any  possible  line  drawn  through  X.  If  then  the 
line  XA'B  is  drawn  through  X  and  A'  intersecting  AP"  at  B, 
the  ordinate  AB  will  represent  the  counter  e.m.f .  developed  when 
the  current  has  been  increased  from  150  to  200  amp.  without 
changing  the  speed.  The  ordinate  S"B  gives  the  total  IR  drop 
and  EB  that  external  to  the  motor;  this  latter,  divided  by  the 
current,  determines  the  new  value  of  resistance.  The  IR  drop 
will  then  decrease  along  the  line  BBf  as  the  current  falls  off,  until, 


500 


100  EOO 

Motor  Amperes. 

FIG.  57. — Volt -ampere  diagram  for  determining  resistance. 

at  point  B' ',  the  current  must  be  increased  again.  The  same 
construction  is  repeated  until  the  two  motors  are  in  series  without 
resistance.  The  current  which  will  be  obtained  when  the  last 
point  of  resistance  is  cut  out  may  be  readily  determined,  since  the 
IR  drop  in  the  motor  alone  is  plotted  as  SE.  When  the  last  line 
radiating  from  X  is  drawn  it  will  intersect  this  line  at  some  point 
as  E".  The  abscissa  determines  the  current. 

In  changing  to  parallel,  it  is  only  necessary  to  move  the  axis  of 
reference  for  IR  drop  to  the  proper  point,  in  this  case  the  ordi- 
nate for  500  volts,  and  continue  the  construction  from  that  place. 
The  remainder  of  the  diagram  is  exactly  the  same  as  before. 

As  explained,  the  diagram  is  theoretically  correct,  and  a  com- 
parison of  the  values  found  graphically  for  resistances  with  those 
calculated  in  Table  I  shows  how  closely  they  agree.  Further, 


CONTROL  OF  RAILWAY  MOTORS 


111 


the  diagram  may  be  used  for  any  value  of  line  potential  without 
other  change  than  shifting  the  origin  for  the  IR  drop.  For 
different  current  limits  it  is  necessary  to  take  other  points  on  the 
tractive  effort  per  ampere  curve,  thus  getting  a  new  location  for  X. 
The  shape  of  the  curve,  as  drawn  on  the  diagram,  shows  that  a 
small  variation  may  be  made  without  relocating  this  point,  and 
the  error  will  not  be  great. 

In  general,  as  the  resistors  are  used  both  for  the  series  and  the 
parallel  connections,  a  certain  amount  of  adjustment  must  be 
made  of  the  values  deter- 
mined for  definite  current 
limits.  The  method  of  doing 
this  may  be  seen  at  once 
from  the  construction.  It  is 
only  necessary  to  continue 
the  IR  lines  either  above  or 
below  the  limits  set,  and  the 
proper  values  can  be  found 
directly. 

If  a  controller  is  to  be  used 
with  four  motors,  the  changes 
in  the  method  to  allow  for 
sets  of  two  motors  perma- 
nently connected  in  series  or 
in  parallel  may  easily  be  de- 
termined. 

Time  for  Operating  Con- 
troller.— In  Fig.  58  is  given  a 
diagram  between  motor 
speed  and  motor  current  for 
each  of  the  points  on  the 
control,  as  computed  in  the 
preceding  problem.  From 

methods  already  outlined,  the  time  when  the  controller  handle 
should  be  moved  from  one  point  to  the  next  may  be  obtained,  if 
the  car  weight  be  known.  For  a  given  equipment,  the  time  for 
operation  of  the  controller  has  been  found,  and  the  relations  be- 
tween current  and  time  are  given  in  Fig.  59.  It  is  noticeable  that 
the  length  of  time  of  operation  on  each  point  of  the  control  is 
different,  the  time  on  the  parallel  points  being  considerably 
greater. 


Current.  Amperes 

FIG.  58.— Speed  curves  for  resistance 

points. 

These  curves,  \vith  the  exception  of  the  "Full 
Series"  and  the  "Full  Parallel"  positions,  are 
similar  to  that  in  Fig.  21,  and  may  be  calcu- 
lated in  the  same  manner. 


112 


THE  ELECTRIC  RAILWAY 


With  a  controller  arranged  for  automatic  acceleration,  the 
resistance  will  be  reduced  at  the  proper  time,  and  no  attention 
need  be  given  this  phase  of  its  action.  With  hand  controllers 
the  tendency  is  for  the  motorman  to  rotate  the  operating  handle 
at  a  uniform  rate.  Should  he  do  this,  the  resistances  having  been 
calculated  for  definite  current  limits,  as  outlined  in  the  preceding 


400 
300 

I 
f 

200 

Curre 

nt  per  Ca 

r 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

Cu 

r  rent  per 

Motor 

\ 

-^ 
1 

3 

100 

c 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\x 

\      | 

\i 
\< 

% 

\ 

\ 

V 

\ 

\ 

. 

2 

4                 €> 

Time 

8 

,  Second^ 

10                12 

FIG.  59. — Current-time  curve  for  starting  a  car. 

This  is  the  form  of  curve  obtained  when  the  resistances  and  the  time  of  moving  the  con- 
troller handle  have  been  correctly  determined.  Note  that  the  time  on  the  various  points  is 
not  uniform. 

paragraphs,  the  results  will  be  quite  different.  Fig.  60  gives  the 
values  of  current  obtained  when  the  controller,  with  resistances 
as  determined  previously,  is  rotated  at  a  uniform  rate  such  that 
all  the  resistance  will  be  removed  from  the  circuit  at  the  same  time 
as  in  the  proper  operation.  The  conclusion  is  obvious.  Either 
the  controller  should  be  notched  up  at  the  proper  rate,  or  the 
resistance  should  be  re-calculated  for  a  uniform  length  of  time  on 
each  point. 


CONTROL  OF  RAILWAY  MOTORS 


113 


Resistors  for  Railway  Service. — In  connection  with  the  types 
of  control  already  considered,  it  is  essential  that  proper  resistors 
be  employed.  The  amount  of  energy  to  be  dissipated  is  compara- 
tively large,  and  the  current-carrying  capacity  must  be  consider- 
able. Further,  the  materials  of  which  the  resistors  are  made 
should  be  such  that  continual  service,  calling  for  repeated  heating 
and  cooling,  will  not  cause  injury  to  them. 


400     16 


350     14 


£300     12 

fe        3: 

r 


250    JO 

-'  *S 

s     s. 


^200  "8 


150  6 
100  4 
50  2 


Current 


ren 
Car 


i 


Current 


4  6          a 

Time,  Seconds. 


10 


FIG.  60. — Starting    current   with   improper   operation    of    controller. 

The  time  increments  on  the  successive  points  are  uniform.  Note  that  while  the  average 
value  of  the  current  is  practically  the  same  as  in  Fig.  59,  it  varies  over  a  wider  and  non-uni- 
form range;  and  the  speed-time  curve  is  not  smooth. 

In  early  equipments  the  resistors  were  chosen  merely  to  give 
the  proper  resistance,  without  regard  to  their  other  qualities.  A 
favorite  type  consisted  of  strips  of  German  silver,  interlaid  with 
strips  of  mica,  and  rolled  up  into  spirals.  These  were  expensive, 
and  heavy  overloads  would  tend  to  burn  them  out.  An  improve- 
ment was  introduced  by  ventilating  the  coils;  but  this  did  not 
make  them  very  successful.  They  have  been  entirely  superseded 


114 


THE  ELECTRIC  RAILWAY 


for  regular  service  by  resistors  of  the  cast  grid  type.  The  grids 
are  made  of  cast  iron,  or  of  iron  alloys,  and  are  assembled  in  light 
frames  in  units  of  the  proper  capacity,  as  shown  in  Fig.  61.  The 
grids  are  entirely  open  to  the  air,  and  if  placed  under  the  car  or 
locomotive  in  such  positions  as  will  allow  currents  of  air  to  reach 
them,  they  are  entirely  satisfactory.  They  are  cheap  and  reliable, 
and,  although  the  temperature  coefficient  is  not  negligible,  it 
makes  little  difference,  for  it  can  be  determined  and  allowed  for. 
A  recent  variation  of  the  grid  resistors  is  in  making  them  of  steel 
bar,  bent  to  the  proper  shape  and  afterward  case-hardened,  in- 
stead of  cast  iron.  This  removes  the  greatest  objection  to  the 
cast  grid — brittleness — while  not  changing  the  other  properties  to 
any  extent. 


FIG.  61. — Assembled  frame  of  grid  resistors,  and  separate  unit. 
The  resistors  used  with  railway  motor  control  are  of  this  or  similar  types.     They  are 
made  of  cast  iron  in  the  form  of  grids,  and  assembled  in  frames,  as  shown. 

A  type  which  has  found  some  favor,  especially  in  connection  with 
polyphase  induction  motor  control,  is  the  liquid  or  electrolytic 
resistor.  A  tank  of  the  proper  size  and  shape  is  provided  with 
two  metal  electrodes  and  is  filled  with  brine  or  other  electrolyte. 
One  of  the  electrodes  is  movable,  so  that  the  distance  between 
them,  and  hence  the  resistance,  may  be  changed  by  fine  grada- 
tions. The  acceleration  does  not  have  abrupt  variations,  such 
as  must  necessarily  be  occasioned  when  a  limited  number  of  fixed 
resistances  are  used.  The  water  resistor  is  cheap,  and  is  capable 
of  getting  rid  of  a  large  amount  of  heat,  since  the  temperature  of 
the  electrolyte  cannot  increase  beyond  the  boiling  point,  the 
generation  of  heat  at  that  point  causing  ebullition  of  the  electro- 
lyte, releasing  energy  in  the  vapor. 


CONTROL  OF  RAILWAY  MOTORS 


115 


Control  of  Single -Phase  Motors. — Single-phase  series  motors 
can  be  controlled  by  the  ordinary  series-parallel  method  just 
described.  Owing  to  the  fact  that  the  main  justification  for  the 
single-phase  motor  is  in  the  high  trolley  potentials  which  may  be 
employed,  it  is  necessary  to  use  a  stationary  transformer  on  the 
car  or  locomotive  to  reduce  the  pressure  to  a  value  suitable  for 
operation  of  the  motors.  This  makes  it  possible  to  get  an  efficient 


Trolley 


FIG.  62. — Transformer  control  for  single-phase  motors. 

The  motor  performance  is  varied  by  connecting  the  machines  to  the  different  taps,  1,  2, 
3,  etc.  in  turn. 

method  of  potential  variation  simply  by  bringing  out  from  the 
secondary  of  the  transformer  a  number  of  taps  which  may  be  con- 
nected in  turn  to  the  motors.  A  controller  of  this  type  is  shown 
diagrammatically  in  Fig.  62. 

Owing  to  the  high  efficiency  of  the  transformer,  each  step 
on  the  controller  may  be  used  as  an  operating  point,  there  being 
no  loss  due  to  the  use  of  resistance,  as  with  direct-current  con- 
trol. The  motors  are  ordinarily  placed  permanently  in  parallel 


116 


THE  ELECTRIC  RAILWAY 


or  in  series-parallel,  and  the  entire  variation  in  potential  is  ob- 
tained by  changing  the  transformer  taps  to  which  the  motors 
are  connected. 

In  order  to  obviate  breaking  the  circuit  in  shifting  from  one  tap 
to  the  next,  connection  is  made  through  a  " preventive  coil," 
which  is  a  coil  of  wire  on  a  magnetic  core,  designed  to  have 
approximately  the  same  e.m.f.  as  the  portion  of  the  transformer 
winding  it  short-circuits.  The  lower  terminal  of  the  coil  may 
then  be  disconnected  and  reconnected  to  the  next  higher  tap 
without  causing  any  disturbance  in  the  system.  The  method  is 
shown  in  detail  in  Fig.  63.  For  the  heavier  equipments  a  double 


To  Trolley 


To  Motors 


FIG.  63. — Use  of  the  preventive  coil. 

By  the  use  of  the  preventive  coil  the  motors  may  be  connected  to  the  various  taps  on  the 
transformer  without  breaking  the  circuit,  and  without  any  wide  variation  in  tractive  effort 

set  of  preventive  coils  is  used,  making  the  operation  still  more 
smooth. 

An  induction  regulator  can  be  employed  for  varying  the  po- 
tential on  the  motors  of  a  single-phase  equipment,  as  shown  in  Fig. 
64.  This  allows  an  absolutely  uniform  acceleration.  Its  use 
was  proposed  when  the  single-phase  system  was  first  projected; 
but  experience  has  proved  that  the  acceleration  obtained  with  taps 
from  the  main  transformer  is  smoother  than  in  series-parallel 
control  of  direct-current  motors  with  the  same  number  of  steps, 
and  the  use  of  the  regulator  has  been  unnecessary.  In  some  of 
the  larger  European  single-phase  locomotives  it  has  been  em- 
ployed with  considerable  satisfaction. 

Combination  Systems  for  Single  Phase  and  Direct  Current. — 
Since  the  single-phase  series  motor,  when  conductively  compen- 
sated, is  also  an  excellent  direct-current  motor,  it  may  be  oper- 


CONTROL  OF  RAILWAY  MOTORS 


117 


ated  equally  well  on  a  single-phase  alternating-current  circuit  or 
on  a  direct-current  circuit,  provided  the  line  pressure  be  correct. 
A  number  of  the  heavier  single-phase  equipments  are  arranged 
for  both  methods  of  operation.  All  that  is  necessary  is  to  have 
proper  controllers  for  each  kind  of  current,  and  switches  for 
changing  circuits  as  the  train  passes  from  one  source  of  supply 
to  the  other,  as  shown  in  Fig.  65.  It  is  essential  to  guard  against 
the  possibility  of  wrong  connections  on  the  car,  for  an  accidental 


FIG.  64. — Induction  regulator  control  for  single-phase  motors. 

The  transformer  taps  are  replaced  by  an  induction  regulator,  by  means  of  which  the 
motor  potential  may  be  varied  by  infinitesimal  steps. 

contact  of  the  high-tension  alternating  circuit  with  the  series- 
parallel  controller  would  be  disastrous.  To  prevent  this,  the 
main  switch  of  the  car  equipment  is  provided  with  a  retaining  coil 
so  arranged  that  it  will  open  when  the  circuit  is  interrupted. 
Where  the  alternating-  and  the  direct-current  sections  adjoin,  a 
dead  space  is  left  between  the  two  for  a  distance  not  exceeding  a  car 
length.  A  car  may  then  pass  from  one  section  to  the  other  at  full 
speed,  in  which  case  the  main  switch  opens  on  the  insulated  space 
through  lack  of  power  to  operate  the  retaining  coil,  resetting  auto- 
matically for  the  other  form  of  power  after  passing  the  breaker. 

Control  of  Three -Phase  Motors. — Three-phase  motors  require 
entirely  different  forms  of  control  from  those  previously  described. 


118 


THE  ELECTRIC  RAILWAY 

D.C.  Trolley 


FIG.  Q5. — Combined  single-phase  and  direct-current  control. 

A  combination  of  the  transformer  control  for  the  single-phase  circuit  with  rheostatic  for 
the  direct  current.     On  account  of  the  complication,  it  is  not  used  so  much  now  as  formerly. 


FIG.  66. — Three-phase  motor  control. 

The  leads  from  the  secondary  winding  are  brought  out  to  collector  rings,  and  short  cir- 
cuited through  a  set  of  variable  resistors. 


CONTROL  OF  RAILWAY  MOTORS 


119 


Three  Phase  Supply 


It  has  already  been  shown  that  reductions  in  the  primary  poten- 
tial are  inadvisable,  since  the  torque  of  an  induction  motor  varies 
approximately  as  the  square  of  the  applied  pressure.  The  motor 
speed  may  be  decreased  without  diminution  of  torque  by  placing 
resistance  in  the  secondary  circuits,  as  shown  in  Fig.  66.  The 
effect  of  such  resistance  is  approximately  the  same  as  when  used 
in  the  armature  circuit  of  the  direct-current  shunt  motor,  the 
torque  for  a  given  value  of  current  being  obtained  at  a  lower 
speed  when  resistance  is  introduced. 
This  method  is  open  to  the  same  objec- 
tions as  the  rheostatic  control  for  direct- 
current  motors,  in  that  the  loss  is  great 
at  reduced  speeds.  The  efficiency  of 
an  induction  motor  is  always  slightly 
less  than  the  speed  in  terms  of  syn- 
chronism. A  reduction  of  the  speed  to 
one-half  normal  therefore  decreases  the 
efficiency  to  something  less  than  50  per 
cent.  For  classes  of  service  where  one 
operating  speed  is  sufficient,  and  where 
stops  are  infrequent,  rheostatic  control 
is  applicable;  for  other  cases  one  or 
another  of  the  methods  described  below 
may  be  used. 

Changes  in  Number  of  Poles. — The 
only  type  of  motor  which  can  be  readily 
arranged  to  operate  with  varying  num- 
bers of  poles  is  the  alternating-current 
induction  motor.  The  machine  usually 
has  a  distributed  primary  winding;  and 
it  is  possible,  by  proper  interconnection 
of  the  coils,  to  change  their  grouping  to 
give  two  definite  numbers  of  poles,  one  of  which  is  twice  the  other. 
One  method  of  doing  this  is  shown  in  Fig.  67.  Also,  on  account  of 
the  construction  of  the  primary,  the  coils  being  distributed  in  slots 
around  the  periphery,  two  or  more  distinct  windings,  each  giving 
any  desired  number  of  poles,  may  be  placed  on  the  machine. 
Each  of  these  may  have  its  coils  grouped  to  give  two  sets  of  poles 
in  the  ratio  of  2  :1,  so  that  two  windings  may  be  arranged 
to  give  four  sets  of  poles.  The  speed  of  an  induction  motor  de- 
pends almost  entirely  on  the  frequency  of  the  supply  and  the 


FIG.  67. — Arrangement 
of  induction  motor  for  two 
sets  of  poles. 

This  is  used  to  give  two  effi- 
cient operating  speeds  for  the  in- 
duction motor. 


120  THE  ELECTRIC  RAILWAY 

number  of  poles,  so  that  this  combination  would  give  four  oper- 
ating speeds.  In  order  to  make  the  arrangement  available,  it 
is  also  necessary  to  wind  the  secondary  of  the  motor  with  the 
same  numbers  of  poles  as  the  primary.  On  account  of  the  com- 
plication when  several  different  windings  are  placed  on  the  sec- 
ondary, the  usual  limit  is  two  numbers  of  poles.  In  case  a  squir- 
rel-cage secondary  winding  is  used,  this '  restriction  does  not 
apply,  and  the  same  secondary  will  work  fairly  well  for  any  com- 
bination. The  squirrel-cage  rotor  is  not  very  satisfactory  for 
traction,  and  is  seldom  used. 

Changes  in  Frequency. — The  speed  of  an  induction  motor 
may  readily  be  varied  by  changing  the  frequency  of  the  supply 
circuit.  This  can  be  done  only  through  the  medium  of  a  rotat- 
ing frequency  changer,  so  that  it  is  not  employed  directly.  It 
is  possible,  however,  to  use  the  induction  motor  itself  in  this  ca- 
pacity; and  when  there  are  two  motors  in  the  equipment  this 
permits  a  method  which  is  used  to  some  extent  for  controlling  the 
speed  of  induction  motors  for  railway  service.  In  this  form  the 
connection  is  known  as  " cascade  control,"  " concatenation,"  or 
" tandem  control." 

Concatenation  of  Induction  Motors. — If  the  rotor  of  an  induc- 
tion motor  be  held  still,  and  an  e.m.f.  be  impressed  on  the  pri- 
mary, an  e.m.f.  will  be  induced  in  the  secondary  in  the  same 
manner  as  in  a  stationary  transformer.  The  frequency  in  the  sec- 
ondary will  then  be  the  same  as  that  of  the  supply  circuit.  This 
secondary  e.m.f.  may  be  used  for  any  purpose,  the  same  as  with 
the  ordinary  types  of  polyphase  transformer.  If  the  rotor  be 
revolved  in  the  same  direction  as  the  magnetic  field,  it  will  cut  the 
flux  at  a  lower  rate,  and  the  secondary  frequency  will  be  corre- 
spondingly reduced.  If  the  speed  of  the  rotor  be  increased  to 
synchronism,  the  flux  will  not  be  cut  at  all  by  the  conductors  on 
the  rotor,  and  its  frequency  will  be  zero.  Between  the  limits  of 
synchronous  speed  and  standstill  the  frequency  will  vary  directly 
as  the  drop  in  speed  below  synchronism,  or  the  "slip." 

The  e.m.f.  generated  in  the  secondary  may  be  used  to  furnish  a 
second  motor  with  electric  power.  If  the  first  motor  be  run  at 
half  speed,  the  frequency  of  its  secondary  circuit  will  be  exactly 
one-half  that  of  the  supply;  and  if  the  secondary  have  the  same 
number  of  turns  as  the  primary,  its  e.m.f.  will  be  one-half  the  line 
potential.  The  two  motors  being  electrically  similar,  and  mechan- 
ically coupled  together,  so  that  they  are  forced  to  run  at  the 


CONTROL  OF  RAILWAY  MOTORS 


121 


same  speed  (as,  for  example,  two  motors  on  axles  of  the  same  car) 
the  power  will  be  delivered  by  the  secondary  of  the  first  motor  at 
the  synchronous  speed  of  the  second.  Since  an  induction  motor 
cannot  deliver  any  power  at  synchronous  speed,  the  second 
machine  will  not  take  any  current  from  the  first  save  for  excita- 
tion, and  the  first  motor  in  turn,  having  no  current  in  its  second- 
ary but  the  magnetizing  current  for  the  second,  will  not  deliver 
any  power.  The  system  is  then  in  the  same  state  of  equilibrium 
as  would  be  the  case  were  the  first  motor  running  alone  in  syn- 
chronism. The  speed  of  the  combination  in  this  condition  is, 


FIG.  68. — Connections  for  concatenation  control  of  three-phase  induction 

motors. 

The  secondary  circuit  of  motor  No.  1  is  connected  to  the  primary  of  motor  No.  2,  whose 
secondary  is  short-circuited  through  resistors.  This  arrangement  gives  an  efficient  half- 
speed  running  point,  in  which  respect  it  is  similar  to  the  arrangement  shown  in  Fig.  67. 

however,  exactly  one-half  the  normal  synchronous  speed  of  the 
single  motor. 

If  the  speed  of  the  motors  falls  a  trifle,  the  frequency  in  the 
secondary  of  the  first  one  is  then  slightly  greater  than  one-half  that 
of  the  primary,  and  the  second  will  be  operating  below  synchron- 
ism. The  value  of  the  slip  of  the  second  motor  is  the  difference 
between  the  speed  corresponding  to  the  secondary  frequency  and 
the  actual  speed.  Conditions  are  therefore  right  for  producing 
torque  in  the  second  machine.  This  will  cause  a  power  current 
to  flow  in  the  rotor  of  the  second  motor,  which  in  turn  must  be 
transformed  from  its  primary.  This  power  current  must  of  course 
be  drawn  through  the  first  motor,  and  the  current  in  the  second- 
ary of  the  latter,  reacting  against  its  field  flux,  will  produce  a 
torque.  It  may  be  shown  that  approximately  one-half  the  torque 


122  THE  ELECTRIC  RAILWAY 

is  furnished  from  each  machine.  In  order  to  obtain  still  lower 
speeds,  as  for  starting,  resistance  may  be  introduced  into  the 
rotor  circuit  of  the  second  motor.  This  will  have  the  same 
effect  as  the  insertion  of  resistance  in  the  secondary  of  a  single 
motor. 

When  it  is  desired  to  operate  above  the  half-speed  obtained 
with  the  two  motors  in  tandem,  the  second  one  may  be  cut  out 
of  the  circuit  and  the  secondary  of  the  first  short-circuited,  either 
on  itself  or  through  resistance,  as  necessary.  The  second  motor, 
if  wound  for  the  correct  potential,  may  be  connected  to  the  line 
in  parallel  with  the  first ;  but  since  the  amount  of  power  required 
for  constant-speed  running  is  considerably  less  than  that  for 
acceleration,  the  second  motor  is  ordinarily  left  entirely  out  of 
the  circuit,  the  power  factor  and  efficiency  of  the  single  motor 
being  higher  than  when  the  load  is  divided.  This  arrangement 
also  makes  possible  a  simpler  form  of  controller. 

In  any  case  when  motors  are  connected  in  cascade,  the  syn- 
chronous speed  of  the  set  may  be  determined  from  the  fact  that 
the  effective  number  of  poles  of  the  combination  is  the  sum  of  those 
of  the  two  motors.  For  instance,  if  a  four  pole  motor  is  con- 
catenated with  one  having  six  poles,  the  result  is  the  same  as 
though  a  single  motor  with  ten  poles  were  used,  whichever  ma- 
chine is  connected  to  the  line. 

Split-Phase  Control. — If  a  polyphase  induction  motor  be  con- 
nected to  a  single-phase  supply,  it  will  not  have  any  starting  torque, 
and  will  therefore  remain  stationary.  If,  however,  the  motor 
be  started  by  any  external  means,  it  will  continue  to  run  and  may 
be  used  in  the  same  way  as  though  it  were  operating  on  a  poly- 
phase circuit.  Experiment  has  shown  that  this  effect  is  due  to  a 
transforming  action  in  the  motor  changing  the  single-phase  supply 
to  polyphase.  If  the  terminals  of  the  idle  phase  be  tested,  an 
e.m.f.  will  be  found,  substantially  of  the  same  value  and  in  the 
same  phase  position  as  in  regular  polyphase  operation.  This 
e.m.f.  may  be  utilized  to  furnish,  with  the  single-phase  e.m.f.  of 
the  supply,  a  true  polyphase  circuit  on  which  may  be  operated 
standard  polyphase  apparatus. 

If  an  induction  machine  of  the  type  described  in  the  last  para- 
graph be  placed  on  a  locomotive,  it  is  evident  that  a  single-phase 
contact  line  may  be  used  to  supply  polyphase  motors  for  propul- 
sion, as  shown  diagrammatically  in  Fig.  69.  This  method  is  used 
in  one  important  installation  in  this  country.  The  three-phase 


CONTROL  OF  RAILWAY  MOTORS 


123 


induction  motors  may  be  of  standard  types,  controlled  by  any  of 
the  means  which  have  been  described  above. 

Special  Systems. — A  number  of  special  systems  of  operation 
have  been  tried  at  one  time  or  another.  All  of  them  possess 
points  of  superiority,  and  may  be  used  to  advantage  in  certain 
installations.  The  most  valuable  of  them  are: 

1.  The  " Ward-Leonard"  system. 

2.  Permutator  system. 

3.  Mechanical  rectifier. 

4.  Mercury  vapor  rectifier. 


Resistors 


FIG.  69. — Split-phase  control  for  operation  of  three-phase  motors  from  a 
single-phase  trolley. 

By  this  means  three-phase  induction  motors  may  be  employed  for  railway  service  through 
the  medium  of  the  rotating  phase-converter. 

Ward-Leonard  System. — This  system  of  control,  invented 
by  the  late  H.  Ward  Leonard,  is  in  its  widest  application  suitable 
for  use  on  any  kind  of  supply  circuit  whatever.  The  current 
from  the  contact  line  is  used  to  operate  a  constant-speed  motor- 
generator  set  (Fig.  70),  consisting  of  a  motor  suitable  for  the 
supply  system,  a  separately  excited  direct-current  generator,  and 
an  exciter,  all  mounted  on  the  same  shaft.  The  propulsion  mo- 
tors are  permanently  connected  to  the  generator  through  the 
reverser,  and  operation  is  controlled  by  varying  the  potential. 
This  may  be  done  either  by  changing  the  resistance  in  the  gen- 
erator field  circuit,  or  by  varying  the  field  current  of  the  exciter. 


124  THE  ELECTRIC  RAILWAY 

The  latter  is  the  method  usually  recommended,  since  the  loss  is 
less. 

This  form  of  control  can  be  operated  to  give  absolutely  uni- 
form acceleration,  and  is  applicable  to  any  form  of  supply  circuit. 
The  efficiency  during  acceleration  is  high,  since  the  rheostatic 
losses  are  practically  eliminated.  No  contacts  carrying  heavy 
currents  have  to  be  broken  or  closed  while  the  train  is  in  opera- 
tion, since  the  motor  current  can  be  reduced  to  zero  by  opening 
the  exciter  field  circuit.  The  objection  to  the  system  is  its  great 
weight  and  cost.  For  this  reason  it  never  has  been  used  in  prac- 
tice, and  only  a  few  locomotives  have  been  equipped  with  it. 
Some  recently  adopted  types  of  control  would  indicate  that  the 


Feverser 


Traction 
Motvr, 


FIG.  70. — Ward-Leonard  system  of  control. 

This  method  is  suitable  for  the  operation  of  standard  direct-current  railway  motors  from 
a  single-phase  trolley,  no  matter  what  the  frequency.  A  motor  for  operation  on  any  com- 
mercial circuit  may  be  substituted  for  the  single-phase  machine. 

weight  and  cost  of  the  Ward-Leonard  system  are  not  so  excessive 
as  would  appear  from  the  opinions  of  different  engineers. 

It  should  be  stated  in  this  connection  that  the  Ward-Leonard 
control  is  used  somewhat  extensively  for  mine  hoists  and  simi- 
lar stationary  service. 

Permutator  Control. — A  special  form  of  induction  machine, 
known  as  the  "permutator,"  has  been  brought  out  for  transfor- 
mation from  alternating  to  direct  current. l  It  consists  essentially 
of  an  induction  motor  primary  and  secondary  winding  held 
stationary.  The  secondary  winding  is  similar  to  a  direct- 
current  generator  armature,  and  has  leads  brought  out  to  a  com- 
mutator. Since  the  secondary  is  held  still  with  reference  to  the 

1  A  more  complete  description  of  this  machine  is  given  in  Chapter  XIII. 


CONTROL  OF  RAILWAY  MOTORS 


125 


primary,  the  e.m.f.  generated  by  the  former  has  a  direct  ratio  to 
the  line  potential,  as  in  an  ordinary  transformer.  If  a  set  of 
brushes  be  rotated  on  the  commutator  at  synchronous  speed, 
direct  current  can  be  taken  off,  and  used  to  operate  ordinary 
series  railway  motors.  Any  standard  type  of  direct-current 
control  may  be  employed,  or  the  primary  potential  may  be  varied 
by  taking  different  taps  from  the  lowering  transformer.  A 
locomotive  constructed  on  this  principle  has  been  operated  in 
France  for  some  time,  and  is  said  to  be  very  satisfactory. 

Mechanical  Rectifier.1 — In  place  of  the  permutator,  a  mechan- 
ical rectifier  may  be  employed  for  furnishing  the  means  of  chang- 


Trolley 


Lowering 
Trans 


Traction 
Motors 


FIG.  71. — Mercury  rectifier  control. 

With  the  mercury  vapor  rectifier,  standard  direct-current  motors  may  be  satisfactorily 
operated  from  a  single-phase  trolley.  As  shown,  two  600-volt  machines  are  placed  in  series, 
with  the  middle  point  grounded. 

ing  from  alternating  to  direct  current  for  supplying  the  propulsion 
motors.  The  rectifier  is  in  effect  a  two-part  commutator,  ro- 
tated at  synchronous  speed  by  means  of  a  small  motor.  The 
two  main  segments  of  the  commutator  are  divided  into  several 
sections,  and  connected  through  reactance.  This  prevents  the 
e.m.f.  from  dropping  to  zero  while  passing  from  one  pole  to  the 
other.  A  locomotive  has  been  built,  using  this  method  of  opera- 
tion, but  no  figures  have  been  published  which  would  indicate 
whether  it  has  proved  satisfactory  or  not. 

Mercury  Vapor  Rectifier. — Still  another  system  proposed  for 
railway  operation  is  to  change  from  high-tension  single-phase  cur- 

1  See  also  Chapter  XIII. 


126  THE  ELECTRIC  RAILWAY 

rent  to  direct  current  through  the  medium  of  a  mercury  vapor 
rectifier.  Rectifiers  of  this  type  have  been  built  commercially 
in  large  sizes,  and  are  not  by  any  means  the  delicate  contrivances 
of  several  years  ago. 

During  the  year  1914,  a  trial  equipment  was  placed  in  operation 
for  the  Pennsylvania  Railroad  on  the  single-phase  line  of  the 
New  York,  New  Haven  and  Hartford  Railroad.  This  locomo- 
tive was  equipped  with  standard  direct-current  motors,  operated 
from  a  mercury  vapor  rectifier.  The  connections  are  shown  in 
Fig.  71.  Although  detailed  reports  are  not  yet  available,  the 
equipment  has  been  in  revenue  service  for  several  months,  and  it 
is  stated  that  the  performance  is  exceedingly  satisfactory.  It  is 
evident  that  this  form  of  control  is  a  commercial  possibility;  and 
if  adopted  will  remove  some  of  the  limitations  imposed  on  the 
single-phase  system  on  account  of  its  inability  to  use  standard 
direct-current  motors. 


CHAPTER  VI 
POWER  REQUIREMENTS  AND  ENERGY  CONSUMPTION 

Requirements  of  Train  Operation. — In  the  engineering  work 
necessary  in  connection  with  the  design  and  operation  of  a  rail- 
road, it  is  essential  that  the  amount  of  power  demanded  from  the 
system,  and  also  the  amount  of  energy  required  for  train  move- 
ment, be  accurately  determined,  whatever  the  character  of  the 
motive  power.  For  any  type  of  motive  power,  there  are  certain 
fundamental  relations  which  determine  these  quantities;  and 
from  them  the  proper  selection  of  equipment  may  be  made.  The 
consideration  of  these  relations  has  already  been  made  in  Chapter 
II ;  they  must  now  be  brought  together  to  see  their  connection  in 
the  solution  of  the  problems  at  hand. 

The  quantities  which  have  the  greatest  effect  on  train  operation 
are  its  weight,  the  train  resistance,  both  inherent  and  incidental, 
the  acceleration  and  the  maximum  speed.  These  are  the  essen- 
tial ones;  but  the  length  of  run  has  a  marked  effect,  since  it  may 
change  the  maximum  speed  or  the  acceleration. 

The  maximum  speed  attained  affects  the  power  required  prin- 
cipally by  the  difference  it  makes  in  the  train  resistance,  but 
its  effect  on  the  energy  consumed  is  much  greater,  since  it  is  a 
measure  of  the  energy  input. 

The  train  weight  is  a  determining  factor  in  both  power  and 
energy,  since  the  value  of  either  varies  directly  with  it. 

It  will  be  shown  that  the  acceleration  has  a  great  influence  on 
the  power  required,  but  its  effect  on  the  total  energy  is  very  small, 
save  in  an  indirect  way.  This  must  be  so,  since  the  energy  im- 
parted to  the  train  depends  so  much  on  the  maximum  speed 
attained  during  the  run. 

The  inherent  train  resistance,  while  it  has  some  effect  on  both 
the  power  and  the  energy,  is  in  most  cases  small  in  comparison 
with  other  variables.  The  incidental  resistance,  especially  that 
due  to  grades,  may  affect  the  requirements  more  than  any  other 
factor.  This  is  seen  most  in  operation  of  slow-speed  freight 
trains,  in  which  case  the  acceleration  is  relatively  low. 

127 


128 


THE  ELECTRIC  RAILWAY 


In  order  to  ascertain  the  power  demand,  then,  for  any  specific 
case,  it  is  necessary  to  know  the  values  given  above.  The  deter- 
mination can  be  made  by  the  methods  outlined  in  Chapter 
II. 

"Straight  Line"  Speed-Time  Curves. — It  is  difficult  to  deduce 
an  analytical  relation  between  the  variables  entering  into  the 
power  problem.  The  characteristic  curves  of  motive  powers 
vary  in  a  manner  difficult  to  express  in  a  simple  equation;  and 
the  same  is  true  of  train  resistance.  In  a  large  number  of  prob- 
lems a  need  is  felt  for  a  simple  and  reasonably  accurate  deter- 
mination of  power  requirements.  By  making  a  number  of 
approximate  assumptions  it  is  possible  to  use  a  graphical  treat- 
ment which  is  comparatively  simple. 


80 


60 


f 

20 


0          20          40          60          80          100         IZO 
Time.    Seconds. 

FIG.  72. — Simple  straight-line  speed-time  curve. 

If  we  consider  the  motive  power  to  be  such  that  it  can  supply  a 
constant  tractive  effort  over  a  limited  range  of  operation,  and 
assume  uniform  rates  of  coasting  and  of  braking,  the  problem  is 
reduced  to  a  point  where  a  solution  becomes  practical.  The 
simplest  run  of  this  type  (A,  Fig.  72)  consists  of  acceleration  at 
a  constant  rate  until  it  is  necessary  to  cut  off  the  power  and  apply 
the  brakes.  It  is  evident  that  if  the  rate  of  braking  is  the  same 
for  all  runs,  this  gives  the  minimum  possible  acceleration.  Fur- 
ther than  this,  an  inspection  of  the  diagram  shows  that  the  maxi- 
mum speed  is  exactly  twice  the  average  speed.  Comparing  this 
run  with  the  ideal  run  K,  at  average  speed,  it  will  be  seen  that  the 
distance  covered  is  the  same  in  each,  the  area  of  the  two  dia- 
grams being  the  same. 


POWER  REQUIREMENTS 


129 


If  a  higher  rate  of  acceleration  than  the  minimum  be  used,  it 
will  be  necessary,  in  order  to  cover  the  same  distance  in  the  same 
time,  to  introduce  a  period  of  coasting  (Fig.  73,  run  B).  Such  a 
high  maximum  speed  as  in  run  A  (which  is  reproduced  from  Fig. 
72)  will  not  be  attained,  since  the  train  is  propelled  at  nearly  the 
maximum  speed  for  some  time  by  coasting.  With  still  higher 
rates  of  acceleration  (runs  C  and  D)  the  maximum  speed  is  further 
reduced.  In  certain  runs,  if 'the  amount  of  drifting  is  too  great, 
the  velocity  which  the  train  must  reach  will  again  be  increased,  on 
account  of  the  great  reduction  of  speed  while  coasting.  In  gen- 
eral, the  efficiency  of  the  motive  powe,r  remaining  the  same,  the 
most  effective  run  for  covering  the  given  distance  is  that  in  which 
lowest  value  of  crest  or  maximum  speed  is  attained. 

The  method  outlined  in  the  last  paragraph  shows  a  way  of 
determining  the  most  economical  acceleration  for  any  given  run. 


0  ZO         4Q.        60          &0          100         IZO 

Time,    Seconds. 

FIG.  73. — Influence  of  acceleration  on  speed-time  curve. 

If  a  succession  of  identical  runs  is  taken  as  the  required  service, 
one  acceleration  can  be  found  which  is  most  efficient  for  all  of 
them.  When  the  runs  differ,  the  best  average  rate  can  be  used. 
This  acceleration  having  been  chosen,  it  should  be  used  for  all 
runs,  no  matter  what  their  length. 

Speed-Time  Curves  with  Electric  Motors. — When  we  consider 
applications  of  the  straight  line  speed-time  curve,  we  find  that  in 
most  cases  of  practical  motive  powers,  the  assumed  conditions 
cannot  be  exactly  met.  In  using  electric  motors,  the  uniform 
acceleration  can  be  adhered  to  only  while  the  potential  is  being- 
raised.  After  the  motors  are  operating  directly  on  the  line  there 
is  no  possibility  of  continuing  the  maximum  acceleration;  but 
the  tractive  effort  will  fall  off  as  determined  by  the  characteristic 
curve  of  the  particular  machine  used.  If  the  run  is  short,  this 


130  THE  ELECTRIC  RAILWAY 

will  not  make  a  marked  deviation  from  the  straight  line  curve,  so 
that  for  preliminary  estimates  or  for  analytical  study  the  approxi- 
mate method  remains  useful.  For  the  actual  selection  of  equip- 
ment for  any  individual  case  the  motor  characteristics  must  be 
employed.  The  method  used  for  determining  the  speed-time 
curve  is  that  described  in  Chapter  II,  page  39,  or  any  other 
accurate  way  of  plotting  it.  In  order  to  estimate  the  distance 
covered  by  the  run,  the  distance-time  curve  may  be  obtained  by 
the  use  of  the  integraph,  by  successive  partial  integrations,  or  by 
determination  of  the  distance  increments  from  the  data  used  to 
plot  the  speed-time  diagram.  Curves  of  this  character  are  of  the 
greatest  value,  since  they  show  the  exact  distance  covered  by 
the  train  at  any  portion  of  the  run. 

Current-Time  Curves. — After  the  speed-time  curve  for  any  run 
has  been  plotted,  the  current-time  curve  may  be  found  directly, 
since  there  is  a  definite  relation  between  the  speed  of  a  motor  and 
the  current  passing  through  it,  which  is  invariable.  This  may 
be  seen  at  once  by  an  inspection  of  Fig.  19.  It  must  be  remem- 
bered, however,  that  while  the  motors  of  an  equipment  are  run- 
ning at  reduced  potentials,  or  under  other  abnormal  conditions, 
the  relation  between  speed  and  current  will  not  be  the  same  as  for 
normal  operation,  although  easily  found  at  such  times  by  the 
methods  already  given.  The  current-time  curve  may  then  be 
plotted.  This  curve  is  of  value,  as  indicating  the  load  which  is 
being  demanded  from  the  line,  as  well  as  that  which  is  being 
imposed  on  the  motors. 

Power-Time  Curves. — If  the  line  potential  is  constant,  the 
current  curve  gives  a  measure  of  the  power  drawn  from  the  line  at 
any  instant,  and  its  integral  measures  the  amount  of  energy  used 
for  the  run.  By  this  means  the  performance  of  different  trains  or 
of  different  runs  may  be  compared.  If  the  line  pressure  is  vari- 
able, the  power-time  curve  must  be  obtained  as  the  product  of  the 
current  curve  and  the  pressure.  In  that  case  a  graph  of  the  latter 
should  be  plotted  against  time. 

Use  of  the  Current  and  Power  Curves. — This  series  of  curves  is 
of  great  use  to  the  engineer  in  determining  the  size  of  equipment 
necessary  for  the  generating  and  substations  of  a  road,  and  for  the 
size  of  transmission  and  feeder  wires.  For  this  purpose  current- 
time  or  power-time  curves  must  be  plotted  for  a  day,  or  such 
other  period  as  covers  the  entire  range  of  load.  The  sum  of 
the  instantaneous  current  values  gives  the  total  demand  on  the 


POWER  REQUIREMENTS  131 

power  plant  at  any  given  instant;  so  by  a  process  of  summation 
the  actual  load  curve  for  an  entire  day's  run  or  any  desired 
time  is  determined.  A  study  of  the  territory  in  which  the  road 
is  located  will,  in  conjunction  with  the  current  or  power  curves 
for  individual  trains,  give  an  opportunity  for  dividing  the  line 
into  proper  sections  for  the  location  of  substations.  This  will 
be  considered  at  greater  detail  in  a  later  chapter. 

Motor  Capacity. — The  other  great  use  of  the  current-time  curve 
is  in  the  determination  of  the  capacity  of  the  motors  to  be  used 
for  a  particular  purpose.  There  are  several  different  methods  of 
doing  this.  Of  these,  the  most  direct  is  that  in  which  the  motor 
heating  is  ascertained  from  the  current  and  potential  carried  by 
the  motor  during  the  period  which  the  rating  covers. 

The  ability  of  a  motor  to  carry  load  depends  on  several  differ- 
ent things:  the  form  of  the  characteristic  curves  must  be  correct, 
and  operation  not  extended  beyond  their  proper  range;  the 
temperature  must  not  exceed  some  maximum  value,  as  deter- 
mined by  the  materials  of  which  the  machine  is  constructed, 
and  the  motor  must  not  be  worked  beyond  the  limits  of  commuta- 
tion. In  modern,  well-built  motors,  the  characteristic  curves 
continue  of  proper  shape  beyond  the  ordinary  range  of  operation, 
and  the  commutation,  both  in  direct-current  and  single-phase 
railway  motors,  is  so  good  that  it  need  not  be  a  determining 
factor.  The  heating  of  the  motor  parts  stands  as  the  practical 
limit,  both  for  instantaneous  and  for  sustained  loads.  Modern 
motors  are  usually  constructed  of  fireproof  material,  the  only 
non-metallic  parts  being  the  insulation,  which  consists  very 
largely  of  mica,  asbestos  and  other  heat-resisting  substances. 

Heating  Limits. — Heating  of  the  motor  imposes  limits  of  two 
kinds  to  its  capacity:  instantaneous  or  momentary,  and  con- 
tinuous. If  a  sudden  load  is  placed  on  a  motor,  there  is  a  rush 
of  current,  with  a  consequent  PR  loss  in  all  portions  of  the 
circuit.  If  the  loss  is  sufficient,  it  may  cause  overheating  of  some 
part,  and  burn  out  the  winding  at  that  place.  Or  it  may  be 
great  enough  to  melt  one  or  more  of  the  soldered  connections 
and  open  the  circuit,  with  the  possible  formation  of  an  arc. 
Even  though  the  joints  in  modern  motors  are  all  made  with 
high-grade  tin  solder,  it  sometimes  happens  that  an  overload 
is  so  heavy  as  to  melt  the  solder  at  the  commutator  necks.  The 
natural  safeguard  against  such  damage  is  to  place  in  the  motor 


132  THE  ELECTRIC  RAILWAY 

circuit  an  automatic  circuit-breaker,  or  a  fuse,  set  so  as  to  open 
before  the  motor  is  damaged. 

The  other  heating  limit  is  the  one  on  which  the  normal  rating 
is  based.  Any  electrical  apparatus  has  a  certain  loss  in  convert- 
ing energy  from  one  form  to  another;  and  it  is  this  which,  occur- 
ring within  the  machine,  causes  heating.  Motor  losses  have 
already  been  discussed  in  Chapter  III.  Some  of  them  are  de- 
pendent on  the  current,  others  on  the  potential,  and  still  others 
on  the  speed  of  rotation.  In  general,  however,  the  losses  may 
be  grouped  into  two  classes:  those  which  are  a  function  of  the 
current,  and  those  dependent  on  other  relations.  Those  losses 
due  to  the  current  vary  nearly  as  its  square;  the  remainder 
about  as  the  first  power  of  the  terminal  pressure.  To  get  the 
average  loss  for  a  given  run  will  be  to  determine  the  corresponding 
rate  of  heat  generation,  and  hence  gives  a  means  of  finding  the 
capacity  of  the  motor. 

In  this  country,  railway  and  other  motors  for  intermittent 
service  are  rated  in  two  ways:  by  the  load  they  can  carry  for  one 
hour  or  other  stated  time  with  a  given  temperature  rise,  under 
specified  conditions,  and  by  that  which  they  can  carry  continu- 
ously with  the  same  temperature  rise,  under  other  stated  condi- 
tions. Either  method  assumes  that  the  load  will  be  uniform 
during  the  period  for  which  the  rating  is  made.1 

Character  of  Railway  Motor  Load. — In  general,  it  is  not  possible 
to  maintain  the  load  on  any  machine  at  a  constant  value  in 
service.  In  the  case  of  a  railway  motor,  its  function  is  to  start 
a  train  from  rest,  accelerate  it  to  some  operating  speed,  arid  run 
it  at  that  speed  for  a  greater  or  less  time.  After  this  the  power 
is  cut  off,  the  train  allowed  to  coast  and  finally  come  to  rest 
under  the  action  of  the  brakes. 

An  inspection  of  the  load  curve  shows  that  the  current 
through  the  motor  is  never  constant,  unless  the  run  is  so  long 
that  the  speed  continues  at  the  maximum  for  some  time.  It  is 
not  possible  to  assign  any  average  value  to  it  offhand.  Further- 
more, there  is  a  period  in  every  run  where  the  motors  are  not 
in  operation,  a  portion  of  it  being  while  the  train  is  in  motion 
and  the  remainder  while  it  is  standing  still. 

After  making  a  stop  of  limited  duration,  a  similar  cycle  ensues; 
and  this  will  be  repeated  indefinitely  during  the  entire  time  of 

1  The  accepted  method  of  rating  railway  motors  is  given  in  the  Standard- 
ization Rules  of  the  American  Institute  of  Electrical  Engineers,  1914  edition. 


POWER  REQUIREMENTS  133 

operation,  as  for  a  round  trip,  or  more  frequently  a  whole  day's 
run.  The  succeeding  cycles  of  current  may  not  be  precisely 
the  same,  since  the  length  of  individual  runs,  the  maximum 
speeds  possible,  and  the  physical  limitations  of  grades,  curves 
and  wind  may  vary.  But  the  general  nature  of  the  cycle  re- 
mains the  same  in  all  cases.  If  it  is  desired  to  depict  the  per- 
formance of  a  railway  motor,  it  is  necessary  to  plot  a  series  of 
current-time  curves  for  a  long  period  of  operation,  say  for  a  round 
trip.  Such  a  current-time  curve  is  shown  in  Fig.  74. 

Methods  of  Equating  Motor  Load. — In  order  to  use  the  data 
from  the  actual  operation  of  the  motors,  as  determined  by  the 
current-time  and  power-time  curves,  it  is  necessary  to  find  some 
basis  on  which  they  may  be  equated  to  constantly  applied  loads. 
This  is  essential  both  for  purposes  of  testing  and  for  the  proper 
selection  of  motors  for  a  given  service.  The  oldest  way  was  by 
comparison,  an  equipment  being  selected  for  a  proposed  road  be- 
cause it  had  given  satisfaction  in  a  similar  service,  possibly  in 
another  locality.  Although  this  method  is  crude,  it  was  used 
for  want  of  a  better,  and  it  must  be  admitted  that  very  good 
results  have  been  obtained. 

The  scientific  method  of  getting  the  equivalent  rating  is  to 
determine  the  potential  and  current  which,  constantly  applied, 
will  produce  the  same  load  on  the  motor  as  the  variable  one  ob- 
tained in  service.  Since  heating  is  the  principal  condition  which 
determines  motor  capacity,  it  is  evident  that  at  the  equivalent 
load  it  must  be  the  same  as  that  in  service.  The  determination 
of  this  load  depends  on  the  use  of  a  method  which  will  find  the 
proper  relations  between  the  variable  current  and  potential  and 
their  equivalent  constant  values  to  give  the  same  heating  in  the 
motor. 

Heating  Value  of  the  Current.1 — In  any  electric  circuit,  there 
is  a  certain  loss  due  to  the  passage  of  the  current  through  resis- 
tance. This  loss  is  a  function  of  the  current,  the  time,  and  the 
resistance.  It  is  always  proportional  to  the  square  of  the  in- 
stantaneous value  of  current,  i,  into  the  resistance  in  ohms,  r, 
being  numerically  equal  to  izr. 

With  the  current  remaining  constant  at  a  value  I  for  any 
definite  interval  of  time,  as 

1  This  discussion  follows  the  method  of  C.  O.  MAILLOUX,  "Methode  de 
determination  du  courant  constant  produisant  le  meme  echauffement 
qu'un  courant  variable,"  International  Electrical  Congress,  Turin,  1911. 


134  THE  ELECTRIC  RAILWAY 

t  =  ti  -  tQ 

the  amount  of  energy,  W,  dissipated  as  heat  in  the  resistance 
r  is 

.     W  =  Pr  (^  -  t0)  =  Prt  (1) 

When  the  current  varies  during  the  time  considered  the  loss 
becomes,  calling  the  instantaneous  value  of  current  i, 


W  =    I    i 

Jo 


i2rdt  (2) 

Jo 

If  the  resistance  loss  is  the  same  in  the  two  cases,  we  may 
equate  the  expressions  (1)  and  (2): 

W  =  Prt  =    I    Prdt  (3) 

from  which  we  may  determine 

pt  =  fm  (4) 


(6) 

Equations  (5)  and  (6)  give  the  important  relations  between  the 
equivalent  constant  and  variable  currents  producing  the  same 
heating  in  the  same  time  interval.  From  equation  (5)  it  may 
be  seen  that  their  squares  are  equal,  and  equation  (6),  that  the 
so-called  "effective"  current  is  equal  to  the  square  root  of  the 
mean  of  the  squares  of  instantaneous  values. 

The  problem  of  equating  a  variable  current  to  a  constant  one 
thus  resolves  itself  into  finding  an  effective  value  which  is  numer- 
ically equal  to  the  square  root  of  the  mean  of  the  successive 
ordinates  of  the  curve  representing  the  function  i2  =  f(t).  If 
the  equation  of  this  function  is  known,  the  determination  is 
simple;  but  if,  as  is  usually  the  case,  it  cannot  be  obtained, 
some  approximate  construction  must  be  resorted  to. 

Determination  of  Effective  Current  from  I2  Curve. — The  gen- 
eral form  of  the  graph  of  current  as  a  function  of  time  is  shown  in 
Fig.  74,  which  represents  a  curve  of  this  character.  Such  a 
chart  may  be  drawn  by  a  recording  ammeter,  or  by  taking  a  large 
number  of  successive  readings  and  plotting  the  curve  therefrom. 


POWER  REQUIREMENTS 


135 


To  apply  the  method  indicated  by  equation  (6)  for  getting  the 
equivalent  current,  the  values  of  i  in  the  current-time  curve  must 
be  squared  and  re-plotted,  as  shown  in  Fig.  75.  The  more  rapid 
the  fluctuations  of  the  original  curve,  the  closer  together  the 


800 


SJ600 
400 


200 


0 


40 


120 


160.       ZOO        240         2?>0        320 
Time,  Seconds. 

FIG.  74. — Typical  current-time  curve. 

This  represents  the  actual  form  of  curve  obtained  in  rapid-transit  service  with  frequent 
stops. 

points  should  be  taken,  since  the  effect  of  squaring  is  to  greatly 
magnify  the  differences  between  succeeding  values. 

The  area  under  the  curve,  as  Fig.  75,  must  next  be  found  by 
some  form  of  mechanical  integration,  as  the  use  of  a  planimeter. 


80,000 


;  60,000 


\S) 

g  40,000 


'20,000 


40 


80 


120         160        200       240        2&0       320         360 
Time,  Seconds. 

FIG.  75. — Current  squared-time  curve. 

This  curve  is  produced  by  squaring  the  values  of  the  current  shown  in  Fig.  74. 

This  area,  divided  by  the  total  length  of  the  diagram,  gives  the 
mean  ordinate,  P.  It  is  necessary  to  use  the  same  units  of  linear 
and  square  measure,  for,  if  the  planimeter  gives  the  area  in  square 


136 


THE  ELECTRIC  RAILWAY 


inches,  the  length  of  the  base  should  be  taken  in  inches,  and  the 
quotient  will  give  the  average  height  in  inches.  This  is  some- 
times forgotten  in  interpreting  the  results.  The  square  root  of 
this  mean  ordinate,  when  reduced  to  the  scale  of  the  curve,  is 
the  effective  value  desired,  as  /  in  equation  (6). 

Determination  by  Polar  Method. — The  second  method,  which 
was  elaborated  by  Mr.  Mailloux  in  the  paper  above  referred  to 


45 


00 


3--oo 


45 


S.-oo 


4:00 


45 


FIG.  76. — Polar  current-time  diagram. 

This  represents  the  same  function  as  Fig.  74,  but  replotted  in  polar  coordinates. 

obviates  the  necessity  of  plotting  a  curve  of  values  of  current 
squared,  replacing  it  by  a  polar  diagram  of  current,  Fig.  76, 
which,  while  giving  the  same  final  result,  is  simpler  to  construct. 
The  use  of  the  polar  curve  for  finding  the  heating  due  to  a 
current  originated  with  Dr.  Fleming,1  who  employed  it  for  de- 
termining the  effective  value  of  the  alternating  current.  The 
method  of  Mr.  Mailloux  is  based  on  the  same  principles,  but  is 
wider  in  scope,  including  the  evaluation  of  any  currents,  as  indi- 
cated in  equation  (6). 

1  J.  A.  FLEMING,  "The  Alternate  Current  Transformer,"  1896,  Vol.  I,  §32, 
pp.  190-194,  "Representation  of  Periodic  Currents  by  Polar  Diagrams." 


POWER  REQUIREMENTS  137 

The  first  step  in  this  method  consists  in  plotting  the  current- 
time  curve  on  a  polar  basis,  as  shown  in  Fig.  76.  In  doing  this 
the  current,  i,  being  the  independent  variable,  is  made  the  radius 
vector,  and  the  time,  t,  becomes  the  angle. 

To  make  the  transformation  of  coordinates  complete,  the 
following  condition  must  be  met,  and  that  only: 

f(nAt)  =  f(nAO)  (7) 


for  all  values  of  n  included  between  the  limits  n  =  0,  and  n  =  —  > 

At 

when  t  is  the  total  length  of  the  diagram  in  rectangular  (or  any 
form  of  Cartesian)  coordinates.  If  this  requirement  is  met,  an 
ordinate  y  of  the  rectangular  curve,  at  any  distance  from  the 
origin  along  the  X-axis  and  represented  by  nAt,  will  always  be 
equal  to  the  radius  vector,  p,  of  a  polar  curve,  situated  at  a  pro- 
portional angular  distance,  by  nA0.  It  may  be  seen  at  once  that 
this  relation  is  independent  of  the  values  given  to  AZ  or  to  A0, 
proportional  changes  in  these  affecting  only  the  scale  of  the  curve. 
The  polar  curve  has  different  properties  from  the  rectangular 
curve;  since  it  is  this  difference  which  is  utilized,  the  character- 
istics of  the  polar  curve  must  be  determined.  Of  these,  the  most 
important  for  the  present  purpose  is  the  area  included  by  the 
curve.  An  element  of  the  polar  diagram  contained  between  two 
radii  vectores,  OP  and  OQ  (Fig.  76),  has  an  area  dA, 

dA  =  Y2Pds  =  %P2d8  (8) 

p  being  the  radius  vector,  dO  the  vectorial  angle,  and  ds  =  pdd 
any  element  of  the  curve.  When  the  entire  vectorial  angle  in- 

cluded is 

/j        i          i 

0    =    <Pl    —    <P2 

the  area,  A,  is  equal  to 

A  =   C'dA  =  %  fep*d8  (9) 

•'o  *^o 

This  area  may  be  found  by  mathematical  substitution,  where 
practicable,  or  by  mechanical  integration  in  any  case,  as  by  the 
use  of  the  planimeter. 

For  polar  curves,  as  for  Cartesian  curves,  there  may  be  found 
an  equivalent  area  which  corresponds  to  a  constant  mean  height. 
Using  this  ordinate  and  the  same  total  vectorial  angle,  a  polar 
diagram  will  be  obtained  having  the  same  area  as  that  included 
by  the  actual  curve.  In  Cartesian  coordinates  this  equivalent 
diagram  is  a  parallelogram;  in  polar,  the  sector  of  a  circle. 


138  THE  ELECTRIC  RAILWAY 

The  area  of  the  equivalent  sector,  with  a  vectorial  angle  6, 
and  mean  ordinate  Ip,  being  represented  by  A,  we  have 

A  =  nr 

Equating  this  with  equation  (9), 


(11) 
^  t/o 

from  which  is  reduced 


A  comparison  of  equations  (6)  and  (12)  shows  them  to  be  of 
precisely  the  same  form.  The  two  equations,  one  in  Cartesian 
coordinates,  and  the  other  in  polar,  give  two  ways  of  obtaining 
identical  results.  Using  both  methods  for  the  solution  of  the 
same  problem,  we  may  say  that  I  =  Ip,  so  that 


W  (13) 

Although  the  result  reached  by  equations  (6)  and  (12)  is  the 
same,  there  is  the  important  difference  that  while  equation  (12), 
or  the  member  to  the  right  of  the  equality  sign  in  equation  (13), 
is  the  mean  ordinate  of  a  polar  curve,  equation  (6)  ,  or  the  left  of 
equation  (13),  does  not  represent  the  mean  ordinate  of  the  curve 
of  squares,  but  the  square  root  of  that  value.  The  mean  ordinate, 
I2,  of  the  curve  of  squares  in  rectangular  coordinates,  i2,  is  given 
in  equation  (5).  It  may  be  accounted  for  by  squaring  both  sides 
of  equation  (13),  which  gives 


(14) 
Referring  to  equation  (5),  and  substituting,  we  have 

*de  (15) 


=  i  f'p* 

v  */o 


72  represents  the  mean  ordinate  of  the  rectangular  curve  of 
squares  of  the  function  i.  At  the  right  of  the  equation  is  the  cor- 
rect equivalent  of  7P2,  as  may  be  seen  by  reference  to  equation  (11). 
In  other  words,  the  mean  ordinate  of  a  curve  of  squares  in  Cartesian 
coordinates  is  equal  to  the  square  of  the  mean  ordinate  of  the  polar 


POWER  REQUIREMENTS  139 

curve  representing  the  same  function.  It  may  equally  well  be 
stated  that  the  mean  ordinate  of  the  polar  curve  of  a  function, 
being  the  radius  of  a  sector  subtending  the  same  vectorial  angle 
and  enclosing  the  same  area  as  the  curve,  is  equal  to  the  square 
root  of  the  arithmetical  mean  of  the  squares  of  the  ordinates  of 
the  same  function,  either  represented  by  the  polar  curve  itself, 
or  by  the  corresponding  curve  in  rectangular  coordinates. 

The  expression  just  derived  is  general.  The  value  of  t,  as  used 
in  equation  (6),  may  be  anything;  the  length  of  the  diagram  is 
hence  indefinite,  whether  plotted  in  rectangular  or  in  polar 
coordinates.  The  radius  vector  p  may  make  less  than  one,  or 
any  number  of,  revolutions  about  the  pole.  If  the  vectorial 
angle  is  equal  to  27r,  the  radius  vector  has  made  one  complete 
turn. 

As  the  length  of  the  rectangular  diagram  is  increased,  the  vec- 
torial angle  becomes  correspondingly  larger.  The  scale  chosen 
for  the  polar  diagram  may  be  anything  convenient,  and  the  radius 
vector  may  make  any  required  number  of  turns.  In  order  to 
prevent  confusion,  it  is  preferable  to  use  a  distinct  pole  for  each 
revolution  of  the  radius  vector. 

Replacing  in  equation  (15)  the  value  at  the  right  of  equation 
(10),  we  have 

f-T  (16) 

or,     equally     well, 


The  square  root  of  this  expression  is 

I2A 


(18) 

This  equation  indicates  a  practical  method  for  finding  the  value 
of  Ip,  the  mean  ordinate  (mean  radius  vector)  of  the  polar  curve. 

The  area,  A,  of  a  polar  curve  may  be  obtained  readily  by  a 
planimeter.  The  value  of  &,  the  vectorial  angle,  must  be  numer- 
ically equal  (i.e.,  in  radians)  to  the  number  of  times  2?r  that  the 
radius  vector  has  made  turns  around  the  pole. 

To  use  the  polar  method  of  evaluating  the  motor  load,  the 
current-time  curve  must  be  re-plotted  with  polar  coordinates. 
The  simplest  method  is  to  keep  the  scale  of  ordinates  (amperes) 
the  same,  and  use  any  convenient  value  of  angle  to  represent  the 


140  THE  ELECTRIC  RAILWAY 

abscissa  (time).  As  has  been  shown,  the  latter  scale  is  imma- 
terial; and  the  total  vectorial  angle  may  be  so  chosen  as  to  make 
the  transformation  easy.  For  example,  the  use  of  1°  of  angle 
to  represent  1  second  of  time,  or  other  simple  relation,  makes 
the  construction  of  the  polar  diagram  easy,  since  ordinates  of 
the  rectangular  curve  may  be  transferred  directly  with  the  use 
of  dividers,  no  computation  being  required.  Having  transformed 
the  curve  into  polar  coordinates,  the  area  may  be  found  with  a 
planimeter  or  by  any  other  available  method.  This  quantity 
must  be  substituted  in  equation  (18)  to  get  the  value  of  Ip.  It 
must  be  remembered  that  the  vectorial  angle  must  be  taken  in 
radians.  The  final  result  in  amperes  is  found  by  multiplying  the 
value  of  Ip  by  the  scale  of  the  curve,  based  on  the  units  in  which 
the  area  is  determined.  For  example,  if  the  area  is  found  in 
square  inches,  Ip  will  be  in  inches,  and  the  result  must  be  multi- 
plied by  the  number  of  amperes  per  inch  to  get  the  value  of  the 
r.m.s.  current. 

Average  Motor  Potential. — In  any  run  with  a  normal  set  of 
motors,  the  train  starts  from  rest,  and  is  brought  up  to  about 
half  the  maximum  speed  at  a  nearly  constant  value  of  current. 
This  is  accomplished  by  operating  at  reduced  pressure  during  the 
accelerating  period.  It  is  evident  that  the  average  potential  on 
the  motor  must  be  less  than  that  of  the  line  for  the  time  during 
which  the  motor  is  receiving  power.  There  is  also  a  period  when 
the  motor  is  not  connected,  and  hence  is  not  subject  to  any  e.m.f. 
whatever.  The  iron  loss,  and  to  some  extent,  the  friction  and 
windage,  are  dependent  on  the  value  of  motor  potential.  These 
losses  do  not  vary  as  a  direct  function  of  the  pressure,  but,  on 
the  contrary,  are  nearly  the  same  over  a  wide  range.  For  this 
reason  it  has  been  found  sufficiently  accurate  to  obtain  them  for  a 
few  different  average  values,  such  as  one-half,  three-quarters 
and  full  potential.  Generally  speaking,  the  capacity  of  the 
motor  to  get  rid  of  heat  determines  the  temperature  to  which 
it  will  rise  with  a  certain  amount  of  loss.  This  temperature  is 
largely  independent  of  where  the  losses  are  produced;  that  is, 
if  their  sum  is  a  certain  total,  and  corresponds  to  a  definite 
temperature  rise,  the  same  temperature  will  be  reached  if  the 
distribution  of  loss  between  its  various  components  is  changed. 
Since  the  copper  loss  is  a  function  of  current  only,  it  can  be 
found  by  the  method  outlined.  The  iron  and  friction  losses  are 
more  complex,  and  cannot  be  obtained  readily  except  by  actual 


POWER  REQUIREMENTS  141 

test.  They  do  vary  with  the  terminal  potential,  although  not 
in  direct  proportion.  It  is  evident,  then,  that  if  a  motor  is 
able  to  carry  I  amperes  at  E  volts  with  the  specified  tempera- 
ture rise,  it  will  only  carry  a  less  current,  /',  at  a  higher  po- 
tential E'  depending  on  the  amount  of  increase  in  the  iron  and 
friction  losses.  That  the  variation  in  these  losses  with  the  po- 
tential is  comparatively  small  may  be  seen  by  reference  to  the 
motor  whose  curves  are  given  in  Fig.  19.  This  motor  has  a 
continuous  capacity  of  60  amp.  at  300  volts,  or  of  55  amp.  at  400 
volts.  A  small  error  in  the  determination  of  the  average  poten- 
tial will  therefore  cause  a  relatively  slight  discrepancy  in  this 
connection. 

Rating  of  Railway  Motors. — When  the  heating  value  of  the 
current  has  been  determined,  it  furnishes  a  basis  for  finding  the 
constant  load  which  should  be  applied  to  a  motor  for  purposes  of 
test;  or,  conversely,  that  current  which  the  motor  can  carry  on 
test  represents  the  effective  value  of  the  variable  current  which 
may  safely  be  allowed  in  actual  operation.  In  making  tests  at 
the  factory,  at  least  two  separate  determinations  are  made:  the 
current  which  the  motor  can  carry  for  one  hour  at  normal  poten- 
tial to  obtain  the  maximum  allowable  temperature  at  the  end 
of  this  time,  and  that  which  can  be  applied  continuously,  either 
at  the  line  pressure  or  some  lower  value,  to  give  the  same  maxi- 
mum temperature. 

The  rating  of  railway  motors  has  been  open  to  considerable 
discussion,  on  account  of  the  difficulty  in  specifying  the  average 
or  effective  load  (see  paragraph  on  "  Heating  value  of  the  current") . 
Various  ways  of  determining  the  capacity  have  been  advanced 
at  different  times,  but  none  of  them  has  proved  entirely  satisfac- 
tory. The  present  method  of  rating,  adopted  by  the  American 
Institute  of  Electrical  Engineers  in  1914, l  is  as  follows: 

415.  Nominal  Rating. — The  nominal  rating  of  a  railway  motor  shall 
be  the  mechanical  output  at  the  car  or  locomotive  axle,  measured  in 
kilowatts,  which  causes  a  rise  of  temperature  above  the  surrounding 
air,  by  thermometer,  not  exceeding  90°  C.  at  the  commutator,  and 
75°  C.  at  any  other  normally  accessible  part  after  one  hour's  con- 
tinuous run  at  its  rated  voltage  (and  frequency  in  the  case  of  an  alter- 
nating-current motor)  on  a  stand  with  the  motor  covers  arranged  to 

1  Standardization  Rules  of  the  American  Institute  of  Electrical  Engineers, 
Proceedings  A.  I.  E.  E.,  Vol.  XXXIII,  p.  1281,  August,  1914. 


142  THE  ELECTRIC  RAILWAY 

secure  maximum  ventilation  without  external  blower.  The  rise  in 
temperature  as  measured  by  resistance,  shall  not  exceed  100°  C. 

"416.  The  statement  of  the  nominal  rating  shall  also  include  the 
corresponding  voltage  and  armature  speed. 

"417.  Continuous  Rating. — The  continuous  ratings  of  a  railway 
motor  shall  be  the  inputs  in  amperes  at  which  it  may  be  operated  con- 
tinuously at  one-half,  three-quarters,  and  full  voltage  respectively,  with- 
out exceeding  the  specified  temperature  rises  (see  §420),  when  operated 
on  stand  test  with  motor  covers  and  cooling  system,  if  any,  arranged 
as  in  service.  Inasmuch  as  the  same  motor  may  be  operated  under 
different  conditions  as  regards  ventilation,  it  will  be  necessary  in  each 
case  to  define  the  system  of  ventilation  which  is  used.  In  case  motors 
are  cooled  by  external  blowers,  the  volume  of  air  on  which  the  rating 
is  based  shall  be  given." 

The  first,  or  nominal  rating,  is  the  one  which  has  been  used  for 
many  years  in  this  country  as  expressing  the  output  of  a  railway 
motor.  It  is  not  an  indication  of  the  load  that  the  motor  can 
carry  in  service,  and  is  of  value  mainly  to  give  a  general  compari- 
son of  the  capacities  of  various  machines.  The  second,  or  con- 
tinuous rating,  does  give  an  indication  of  the  ability  of  a  motor  to 
perform  a  specified  service,  and  is  the  one  which  can  be  employed  to 
advantage  in  the  selection  of  equipment. 

It  is  to  be  noted  that  the  continuous  rating,  as  given  in  the  defi- 
nition, includes  provision  for  consideration  of  the  method  of 
ventilation  used.  This  feature  is  very  important.  The  capac- 
ity being  dependent  principally  on  the  heating,  the  motor  will 
have  a  temperature  rise  at  any  specified  load  which  is  determined 
by  the  rate  of  generation  of  heat  due  to  losses  in  the  machine,  and 
the  ability  of  the  motor  to  get  rid  of  the  heat  thus  produced. 
With  natural  ventilation,  the  air  coming  in  contact  with  the  out- 
side of  the  motor  case  constitutes  the  only  medium  available  for 
this  purpose.  If,  by  any  means,  the  quantity  of  air  passing  over 
the  motor  case  is  increased,  the  amount  of  heat  given  off  will  be 
greater,  and  the  temperature  of  the  motor  reduced.  Even  if 
no  ventilating  system  is  provided,  the  rapid  change  of  air  under  a 
moving  train  will  cause  the  motor  to  operate  at  a  lower  tempera- 
ture than  when  tested  in  a  factory  in  still  air.  With  special 
methods  of  ventilation,  in  which  a  quantity  of  air  is  forced  through 
the  motor,  the  temperature  at  the  specified  load  is  still  further 
reduced.  It  follows  that  with  any  system  of  artificial  ventila- 
tion the  rating,  either  nominal  or  continuous,  can  be  increased. 
In  the  rule  for  determining  the  nominal  rating  it  is  expressly 


POWER  REQUIREMENTS  143 

stated  that  no  external  ventilating  system  shall  be  employed,  so 
that  the  gain  in  capacity  applies  only  to  the  continuous  rating. 

In  some  recent  types  of  railway  motors,  the  ventilation  has 
been  improved  by  the  addition  of  blowers  on  the  armature  shaft, 
arranged  to  pass  a  comparatively  large  amount  of  air  through 
the  case  (see  Chapter  IV).  With  motors  of  this  type  the  ven- 
tilating system  is  an  integral  part  of  the  machine,  so  that  the  ad- 
vantage is  not  confined  to  the  continuous  rating,  but  also  serves 
to  increase  the  nominal  rating.  Since  the  latter  is  useful  for 
comparison  only,  this  method  of  ventilation  has  the  effect  of  ap- 
parently giving  a  motor  a  higher  one-hour  capacity  than  when 
the  ventilating  system  is  outside  the  machine  itself. 

Motor  Capacity  and  Selection. — To  use  the  above  information 
in  the  selection  of  a  motor  for  a  definite  service,  it  is  necessary 
to  determine  the  average  current  and  potential  for  the  equipment. 
This  may  be  done  by  finding  the  average  run,  and  plotting  for  it 
the  current  curve  for  a  motor  which  is  expected  to  do -the  work; 
or  by  making  a  set  of  current  curves  representing  the  performance 
of  the  motor  over  an  extended  series  of  runs,  and  getting  the 
average  current  from  them.  In  either  case  the  "root  mean 
square"  (r.m.s.)  current  should  be  found,  which  gives  the  load 
which  the  motor  will  have  to  carry.  If  this  current  is  equal  to 
the  continuous  rating  of  the  motor  at  the  average  potential  found 
for  the  run  or  runs,  the  motor  has  sufficient  capacity  for  the  work, 
unless  it  is  considered  advisable  to  have  a  certain  margin  for 
handling  emergency  business,  as  for  hauling  trailers.  If  the 
r.m.s.  current  is  decidedly  less  than  the  continuous  rating,  it  will 
be  well  to  see  if  a  smaller  motor  can  be  used.  If,  on  the  other  hand, 
the  r.m.s.  current  is  greater  than  the  continuous  capacity,  a 
larger  motor  will  be  needed.  It  is  never  wise  to  attempt  to  load 
a  motor  beyond  its  continuous  rating,  since  there  is  great  liability 
of  permanent  injury.  Practically  any  railway  motor  of  standard 
make  is  able  to  carry  its  rated  continuous  load  without  difficulty, 
and  will  operate  indefinitely  without  trouble  if  this  is  not  exceeded. 
But  if  the  best  of  motors  is  loaded  beyond  the  continuous  capac- 
ity, trouble  is  liable  to  develop,  armatures  to  burn  out,  commuta- 
tors become  rough,  etc. 

Motor  Speeds  and  Gearing. — For  the  smaller  motor  equip- 
ments, such  as  are  used  on  city  and  interurban  cars,  the  motors  are 
almost  invariably  of  the  geared  type.  There  is  considerable 
latitude  in  the  choice  of  gear  reduction  for  any  particular  service. 


144  THE  ELECTRIC  RAILWAY 

Reference  to  the  section  on  " Straight  Line  Speed-Time  Curves" 
at  the  beginning  of  this  chapter  will  show  that  the  same  run  can 
be  covered  in  a  given  time  with  a  wide  range  of  acceleration  rates. 
Since  it  has  been  demonstrated  that  there  is  a  certain  acceleration 
rate  which  is  most  efficient  for  a  given  run,  this  should  be  deter- 
mined and  the  motor  gear  ratio  selected  to  give  it.  In  nearly  all 
practical  runs  this  will  call  for  the  maximum  acceleration  possible ; 
or,  in  other  words,  the  motors  should  be  geared  for  the  lowest 
speed  which  will  enable  them  to  cover  the  distance  in  the  given 
time.  A  higher  speed  will  be  accompanied  with  lower  accelera- 
tion and  less  coasting;  and  since  the  kinetic  energy  of  the  train  is 
being  used  for  propulsion  when  drifting,  the  motors  are  not  called 
on  for  so  great  a  load.  This  is  beneficial,  both  from  the  stand- 
point of  motor  capacity  and  of  energy  consumption.  In  addi- 
tion, the  required  acceleration  may  often  be  obtained  with  less 
current  from  the  line,  so  that  the  demand  on  the  electrical  sys- 
tem, and  the  transmission  and  conversion  losses,  are  reduced. 

For  interurban  cars,  the  same  equipment  is  ordinarily  used 
both  for  local  and  for  limited  trains.  If  the  gearing  is  correct  for 
the  local  runs,  the  maximum  speed  possible  is  ordinarily  too  low 
to  meet  the  demands  of  the  fast  schedule  needed  for  limited  trains. 
If  the  motors  are  geared  for  the  high  speed  demanded  in  limited 
runs,  the  possible  acceleration  for  local  service  will  not  be  enough; 
or  the  heavy  current  will  be  so  great  as  to  cause  overheating. 
Some  roads  have  used  motors  with  a  greater  capacity  than  other- 
wise necessary  in  order  to  standardize  the  equipment. 

Use  of  Field  Control  Motors. — A  more  recent  solution  is  the 
use  of  field  control  motors,  such  as  described  in  Chapter  III. 
With  the  heavy  field  the  tractive  effort  is  sufficient  to  meet 
the  demands  for  rapid  acceleration  in  local  service,  and  for  the 
city  portion  of  limited  runs.  The  weak  field  allows  the  same 
motors  to  be  operated  at  high  speeds  for  the  limited  trains,  and 
for  the  longer  runs  in  local  service.  Both  of  these  results  may 
be  accomplished  with  motors  of  the  minimum  possible  size, 
while  the  power  demand  from  the  line  is  kept  down  to  as  low  a 
value  as  with  the  single-speed  motor  suitable  for  the  same 
service. 

Proper  Number  of  Motors. — A  question  to  be  decided  in  the 
choice  of  motive  power  is  that  of  the  number  of  units  to  be  used 
to  produce  the  desired  results.  It  is  obvious  that  if  the  propor- 
tional performance  of  motors  of  all  sizes  were  the  same,  it  would 


POWER  REQUIREMENTS  145 

make  no  practical  difference  into  how  many  units  the  power 
were  subdivided.  In  practice,  with  double-truck  cars,  there  is 
a  choice  between  two  motors  and  four  motors  for  the  equipment. 
The  capacity  of  electric  motors  varies  nearly  as  the  fourth  power 
of  the  linear  dimensions,  so  that  a  motor  of  double  rating  will 
have  its  dimensions  approximately  1.2  times  those  of  the  smaller 
machine,  resulting  in  less  total  weight  for  the  two-motor  equip- 
ment. Since  the  dimensions  are  not  increased  in  proportion  to 
the  output,  the  length  of  windings  and  of  the  magnetic  circuit 
are  correspondingly  less,  and  the  efficiency  is  consequently  higher. 
All  other  things  being  equal,  the  use  of  two  motors  of  a  certain 
rating  should  result  in  a  smaller  input  to  the  car  than  when  four 
motors  of  the  same  total  capacity  are  employed.  From  the 
efficiency  standpoint  there  can  be  no  question  but  that  the  smaller 
number  of  motors  is  preferable.  This  arrangement  also  has 
the  effect  of  simplifying  the  control  wiring,  and  in  some  cases 
allows  a  less  intricate  and  cheaper  controller. 

The  use  of  four  motors  is  defended  on  the  ground  that  there  is 
greater  reliability  with  this  combination,  since  the  damaging  of 
one  motor  only  affects  one-fourth  of  the  total  number.  But  in 
ordinary  types  of  series-parallel  control  the  motors  are  per- 
manently connected  in  pairs,  so  that  when  one  is  injured  its 
mate  has  to  be  cut  out  at  the  same  time.  Neither  is  it  at  all 
certain  that  four  machines,  with  the  necessary  duplication  of 
parts,  both  in  the  motors  themselves  and  in  the  control  and 
wiring,  are  less  subject  to  damage  than  the  two  larger  ones 
which  are  their  equivalent.  It  is  evident  that  the  maintenance 
expense  for  the  four  machines  will  be  greater  than  for  the  two. 
The  cost  of  repairing  does  not  vary  much  with  the  motor  capacity; 
and,  with  equal  wear,  there  are  twice  as  many  parts  to  renew  in 
the  four-motor  equipment. 

The  best  reason  for  the  use  of  four  motors  is  that  the  entire  weight 
of  the  car  is  available  for  adhesion,  so  that  the  maximum  tractive 
effort  possible  with  a  four-motor  equipment  is  greater  than 
with  two  motors.  If  the  car  alone  is  considered,  the  use  of  all 
axles  as  drivers  gives  a  total  adhesion,  depending  on  the  condi- 
tion of  the  track,  of  from  500  Ib.  per  ton  with  a  coefficient  of  25 
per  cent,  to  200  Ib.  per  ton  with  one  of  10  per  cent.  Even  in  the 
worst  cases,  with  wet  and  slippery  track,  it  is  possible  to  get 
an  acceleration  of  approximately  2  miles  per  hr.  per  sec. 

With  the  two-motor  equipment  about  60  per  cent,  of  the  total 
10 


146  THE  ELECTRIC  RAILWAY 

weight  of  the  car  is  on  the  drivers.  The  corresponding  values  of 
maximum  tractive  effort  available  are  from  300  Ib.  per  ton 
with  an  adhesion  coefficient  of  25  per  cent,  to  120  Ib.  per  ton 
with  one  of  10  per  cent.  With  the  worst  conditions  such  an 
equipment  should  be  able  to  give  an  acceleration  of  about  1.2 
miles  per  hr.  per  sec.  This  might  not  be  high  enough  for 
an  extreme  case,  but  in  general  is  sufficient.  If  the  motor  car 
is  to  haul  one  or  more  trailers  the  use  of  four  motors  is  entirely 
justified. 

Another  place  where  the  use  of  four  motors  is  advantageous  is 
where  the  total  motor  capacity  is  so  great  that  the  limit  of  space 
between  the  wheels  and  beneath  the  car  floor  is  reached.  It  is 
quite  practical  to  build  a  single  motor  of  about  180  kw.  capacity 
of  such  dimensions  that  it  can  be  mounted  on  a  car  truck  for 
standard  gauge  track,  with  36-in.  wheels.  It  is  seldom  that  a 
greater  total  capacity  than  360  kw.  per  car  is  needed,  so  that 
this  limitation  is  not  felt  except  in  the  design  of  locomotives. 

It  should  be  noted  that  with  maximum  traction  trucks1  the 
proportion  of  total  car  weight  which  can  be  placed  on  the  drivers 
is  increased  from  60  per  cent.,  as  given  above,  to  from  75  per 
cent,  to  80  per  cent.  Such  trucks  are  used  to  a  considerable 
extent  in  city  service,  but  are  unsuited  to  speeds  much  over 
30  miles  per  hr.,  so  that  their  application  is  confined  to  special 
cases  where  this  speed  will  not  be  exceeded. 

Power  Required  for  Alternating-Current  Motors. — The  fore- 
going discussion  has  been  made  with  special  reference  to  direct- 
current  series  motors,  but  in  nearly  every  particular  it  applies 
equally  well  to  both  single-phase  and  three-phase  motors.  The 
method  of  determining  the  capacity  is  precisely  the  same  for  any 
type  of  motor;  and  the  ways  of  increasing  the  continuous  rating 
by  improving  ventilation  may  be  applied  equally  well  to  all.  The 
relative  performance  of  two-motor  and  four-motor  equipments  is 
identical,  whether  the  machines  be  designed  for  operation  on 
direct  current  or  on  alternating  current.  Curves  showing  typical 
results  for  a  run  with  single-phase  series  motors  are  given  in 
Fig.  77. 

It  has  been  mentioned  previously  that  field  control  is  not 
practical  with  single-phase  series  motors;  nor  is  it  necessary, 
since  the  speed  may  be  varied  by  the  use  of  different  taps  on  the 
transformer. 

1  See  Chapter  VIII. 


ENERGY  CONSUMPTION 


147 


Alternating-current  motors,  as  now  built,  are  not  usually 
employed  for  such  high  rates  of  acceleration  as  are  direct-current 
motors;  but  this  is  largely  because  the  demand  for  alternating- 
current  distribution  is  almost  entirely  in  a  field  where  the  re- 
quired acceleration  is  much  lower  than  in  city  service.  It 
is  quite  possible  to  obtain  the  same  acceleration  with  either 
type  of  motor. 


4^=* 


240 


280 


320 


120  160  200 

Time,  Seconds 
FIG.  77. — Speed-time  and  input  curves  with  single-phase  motors. 

The  effect  of  the  transformer  control  is  shown  in  the  low  value  of  power  input  during  the 
period  of  sub-normal  potential.     Contrast  this  with  Figs.  47  and  48. 

Energy  Required  for  Train  Operation. — We  have  seen  in  the 
preceding  paragraphs  that  a  certain  amount  of  force  is  necessary 
for  the  propulsion  of  trains.  Since  the  application  of  force  re- 
sults in  the  performance  of  work,  a  certain  amount  of  energy  is 
required  for  train  movement,  which  can  be  determined  from 
the  mechanical  relations  taken  up  in  Chapter  II.  The  energy 
required  may  be  divided  into  two  kinds,  as  follows : 

1.  Energy  which  is  not  capable  of  return  to  the  supply 
circuit,  nor  of  use  in  the  propulsion  of  the  train. 

2.  Energy  which  can  be  recovered,  in  whole  or  in  part, 
and  used  for  propulsion,  or  returned   to   the    supply 
system. 

The  energy  under  the  first  head  consists  of  that  used  to  over- 
come fixed  resistances  of  all  sorts.  This  includes  both  the  in- 
herent train  resistance  and  that  due  to  curves  and  natural  winds. 
Losses  in  the  motive  power  are  also  of  this  type. 


148  THE  ELECTRIC  RAILWAY 

The  second  class  includes  the  energy  for  ascending  grades  and 
that  needed  for  the  acceleration  of  the  train.  Energy  of  this 
sort  is  stored  in  the  moving  body,  either  as  kinetic  or  as  potential 
energy. 

In  general,  a  large  share  of  the  stored  energy  is  wasted  in  normal 
train  operation.  It  is  inexpedient  for  a  train  to  descend  a  grade 
at  too  high  a  speed ;  so  that,  if  it  has  been  accelerating  due  to  the 
force  of  a  grade  which  has  been  previously  ascended,  this  ac- 
celeration must  often  be  stopped  by  the  application  of  the  brakes 
before  the  maximum  attainable  speed  is  reached.  The  energy 
of  the  grade  is  then  dissipated  in  friction  of  the  brake  shoes  against 
the  wheels,  and  is  lost.  The  kinetic  energy  of  the  train,  due  to 
its  motion  (^Mv2)  can  be  recovered  and  used  for  propulsion, 
if  it  is  allowed  to  " coast"  or  " drift"  after  the  power  has  been  cut 
off.  The  speed  will  be  reduced  only  so  fast  as  energy  is  taken  out 
of  the  train  to  overcome  the  resistances,  so  that  the  retardation 
will  be  slight.  In  ordinary  operation  it  would  be  impossible  to 
allow  a  train  to  coast  to  a  standstill.  In  this  case  application 
of  the  brakes  will  prevent  the  return  of  energy.  Generally  speak- 
ing, then,  a  certain  amount  of  energy  due  to  the  ascent  of  grades, 
and  to  the  inertia  of  the  train,  is  converted  into  useful  work 
when  descending,  and  in  coasting  to  a  reduced  speed  before  the 
brakes  are  applied. 

Kinetic  Energy. — Since  the  kinetic  energy  of  a  moving  body  is 
proportional  to  the  square  of  its  velocity,  the  amount  of  energy 
which  must  be  supplied  to  a  train  to  accelerate  it  varies  as  the 
square  of  the  maximum  speed  attained  during  the  run.  If  no 
energy  were  wasted  in  train  resistance,  motor  losses,  etc.,  the 
minimum  input  would  be  taken  by  that  run  having  the  lowest 
maximum  speed.  The  limiting  condition  would  then  give  us  a 
run  with  infinite  acceleration  to  the  average  speed,  constant- 
speed  operation  throughout  the  run,  and  finally  infinite  retarda- 
tion to  a  stop  at  the  end  of  the  run.  Such  operation  is  manifestly 
impossible,  since  there  is  a  limit  both  to  the  acceleration  and  to 
the  retardation.  Also,  train  resistance  prevents  motion  at  con- 
stant speed  without  the  application  of  power,  except  under 
certain  conditions.  The  variable  character  of  the  force  exerted 
by  ordinary  forms  of  motive  power  complicates  the  problem  still 
further,  so  that  no  general  equation  covering  all  cases  is  possible. 
Partial  solutions  have  been  made  at  various  times. 


ENERGY  CONSUMPTION 


149 


Use  of  Straight  Line  Speed-Time  Curves. — A  reference  to  Fig. 
72  shows  that  by  considering,  as  in  the  determination  of  power 
requirements,  that  the  motive  power  can  supply  a  constant  tract- 
ive effort  for  a  limited  range  of  speed,  and  that  the  train  resis- 


60  80 

Time,  Seconds 

FIG.  78.  —  Use  of  the  type  run. 


tance  and  braking  rate  are  constant,  we  can  use  the  straight  line 
speed-time  curves  for  a  consideration  of  the  energy  consumption. 
Since  the  energy  required  for  acceleration  is  stored  in  the  motion 
of  the  train,  the  total  amount  required  for  this  purpose  varies  as 


0         30         60         90-       120        150        180        210        240 
Time,  Seconds. 

FIG.  79. — General  locus  of  straight  line  speed-time  curves. 

the  square  of  the  maximum  speed  attained.  If  the  minimum 
acceleration  is  used,  as  in  Fig.  72,  the  energy  imparted  to  the 
train  due  to  its  velocity  must  all  be  absorbed  by  the  brakes  when 
the  train  is  stopped.  If  higher  accelerations  are  employed,  as 


150  THE  ELECTRIC  RAILWAY 

in  Fig.  73,  the  maximum  speeds  are  reduced,  thus  requiring  a 
smaller  energy  input.  The  reason  for  this  is  that  the  train  is 
propelled  while  coasting  by  the  kinetic  energy  which  has  been 
stored  in  it,  so  that  at  the  instant  of  applying  the  brakes  the 
energy  content  is  less  than  in  run  A .  The  most  efficient  run  from 
the  energy  standpoint  is  therefore  roughly  that  in  which  the  train 
has  coasted  to  the  lowest  speed  at  the  time  the  brakes  are  applied. 

Having  determined  the  most  efficient  acceleration,  this  should 
be  used  for  all  runs  made  with  the  same  motive  power  under 
similar  conditions,  irrespective  of  the  length  of  the  run.  This 
may  be  done  by  making  the  different  parts  of  the  run  proportional, 
as  shown  in  Fig.  78. 

By  the  same  method  as  already  used  the  speed-time  curves  for 
any  length  of  run  in  any  time  may  be  determined.  A  series  of 
such  curves  is  given  in  Fig.  79,  and  is  of  value  in  the  investiga- 
tion of  problems  in  train  operation  where  the  motive  power  is 
used  only  for  acceleration. 

Energy  Consumption  with  Electric  Motors. — We  have  already 
seen  that  the  use  of  series  electric  motors  causes  a  variation  from 
the  straight-line  curves.  The  maximum  acceleration  is  only 
continued  up  to  a  limited  velocity;  beyond  that  point  the 
tractive  effort  falls  off,  and  with  it  the  acceleration  becomes  less. 
In  determining  the  actual  energy  consumption  the  most  exact 
method  is  to  plot  the  current-time  curve  corresponding  to  the 
run,  and  from  it  obtain  the  power-time  curve.  From  the  latter 
the  energy  input  to  the  motors  can  be  found  by  summation.  By 
continuing  the  process  of  plotting  the  power  curves  for  the 
entire  period  of  operation,  and  integrating  them,  the  amount  of 
energy  necessary  for  the  propulsion  of  the  train  may  be  deter- 
mined. By  adding  the  inputs  for  all  the  different  trains  on  the 
system,  the  total  energy  consumption  is  found.  In  cases  where 
the  length  of  run  and  the  character  of  profile  do  not  vary  widely, 
the  process  of  integration  may  be  shortened  by  selecting  a  type 
run,  and  deriving  the  total  energy  consumption  from  it.  This 
is  usually  advisable  only  for  preliminary  estimates.  For  final 
calculations  it  is  safer  to  take  the  actual  load  charts  for  deter- 
mining the  total  energy  required. 

Effect  of  Gear  Ratio  on  Energy  Consumption. — It  has  already 
been  shown  that  the  gear  reduction  has  a  considerable  effect  on 
the  load  that  a  railway  motor  is  forced  to  carry.  Similarly,  it  is 
also  a  factor  in  affecting  the  energy  consumption.  We  have  seen 


ENERGY  CONSUMPTION  151 

that,  all  other  things  being  equal,  the  less  the  maximum  speed, 
the  smaller  the  energy  input;  so  that  the  gear  ratio  which  will 
give  the  lowest  maximum  speed  and  make  the  schedule  should 
give  the  least  energy  consumption.  A  certain  qualification  of 
this  statement  must  be  made,  in  that  if  the  gear  reduction  be 
too  great,  the  maximum  speed  may  be  so  low  that  no  coasting 
can  be  included  in  the  run  if  the  schedule  is  to  be  maintained. 
This  may  actually  increase  the  speed  at  which  the  brakes  are 
applied,  so  that  the  energy  which  is  ordinarily  taken  from  the 
inertia  of  the  train  by  coasting  is  all  destroyed  by  the  brakes. 
Such  an  extreme  gear  ratio  is  inadvisable,  since  some  margin 
should  be  allowed  to  take  care  of  heavy  loads,  low  trolley  poten- 
tial, and  other  abnormal  conditions  of  operation.  If  field  control 
motors  are  used,  as  suggested  in  a  previous  paragraph,  the  gear 
ratio  may  be  a  maximum  and  still  give  a  margin  for  taking  care 
of  special  conditions. 

Method  of  Comparing  Energy  Consumption. — In  the  com- 
parison of  equipments,  or  the  same  equipment  under  different 
operating  conditions,  it  is  useful  to  have  some  simple  basis  which 
may  be  used  to  facilitate  computations.  It  is  obviously  im- 
possible to  make  a  complete  set  of  graphical  tests  in  each  case, 
and  yet  it  is  important  to  have  the  comparison  accurate.  It  is 
quite  easy  to  place  a  watt-hour  meter  in  the  motor  circuit,  and 
get  a  record  of  the  total  energy  input  over  an  extended  series  of 
operations.  This  may  then  be  compared  directly  with  the 
energy  for  another  run  of  the  same  length.  The  application 
of  this  method  is  quite  limited,  and  it  is  virtually  impossible  to 
get  consistent  results. 

A  favorite  method  of  comparing  energy  consumption  is  in 
the  use  of  kilowatt-hours  per  car-mile,  or  per  train  mile.  This 
gets  away  from  the  fundamental  difficulty  of  the  direct  com- 
parison, the  variation  in  total  distance,  but  it  does  not  take  into 
account  the  length  of  individual  runs  or  the  weight  of  the  equip- 
ment. It  is  necessary  to  confine  the  application  of  this  method 
to  cars  or  trains  of  approximately  the  same  weight,  and  even 
then  the  results  may  not  be  of  great  value. 

Watt-Hours  per  Ton-Mile. — Since  the  energy  for  moving  a 
given  mass  a  specified  distance  should  be  the  same  with  constant 
train  resistance,  the  best  method  of  comparing  the  energy  con- 
sumption of  different  equipments  is  in  terms  of  watt-hours  per 
ton-mile.  By  this  means  the  weight  is  eliminated,  and  cars  or 


152  THE  ELECTRIC  RAILWAY 

trains  of  widely  varying  mass  may  have  their  energy  consump- 
tion compared  on  a  fairly  rational  basis.  The  effect  of  the 
length  of  run  still  remains;  but  the  calculation  very  often  is  made 
to  determine  the  influence  of  this  variable,  so  that  the  method 
is  directly  useful  in  this  connection. 

To  obtain  the  energy  in  watt-hours  per  ton-mile,  it  is  only 
necessary  to  equip  the  car  with  a  watt-hour  meter  to  record  the 
energy  input,  and  supply  some  means  of  determining  the  average 
weight  of  the  train  and  the  total  length  of  run.  The  result  may 
then  be  reached  directly.  It  is  of  great  value  in  the  comparison 
of  different  equipments  in  various  kinds  of  service.  While  there 
is  a  wide  range  in  the  amount  of  energy  required,  the  limits  are 
fairly  well  defined  for  any  particular  class,  so  that  the  values  ob- 
tained in  different  runs  of  the  same  kind  may  well  be  comparable. 

Influence  of  Train  Resistance  on  Energy  Consumption.  —  A 
certain  portion  of  the  energy  imparted  to  the  train  by  the  motors 
must  always  go  to  overcome  train  resistance.  This  amount  is 
always  equal  to  approximately  twice  the  average  resistance. 
Consider  a  train  moving  at  constant  speed,  V  (miles  per  hour), 
the  total  train  resistance  being  R  (pounds  per  ton).  The  total 
input  in  kilowatts,  P,  is 


The  energy,  W,  in  watt-hours  per  ton-mile,  is 

VR  X  hours  run  X  1000  .     . 

503  T  X  miles  run 

Reducing  this  to  terms  of  unity,  it  becomes 

W  =  R  =  1.995  (21) 


This  equation  holds  under  all  conditions  of  operation,  if  the 
average  value  of  train  resistance,  including  that  due  to  curves, 
be  taken.  This  component  of  energy  does  not  vary  a  great  deal 
in  individual  runs,  unless  the  speeds  differ  widely,  or  the  car 
weights  are  so  dissimilar  as  to  be  incomparable. 

It  is  to  be  noted  that  this  value  of  energy  represents  the  motor 
output  needed  to  keep  the  train  in  motion  at  constant  speed,  with- 
out stops.  This  condition  is  approached  very  nearly  in  long-dis- 
tance runs,  and  gives  the  absolute  minimum  energy  consumption 
for  any  form  of  normal  operation.  For  example,  a  train  consist- 


ENERGY  CONSUMPTION  153 

ing  of  a  single  50-ton  car,  running  at  a  constant  speed  of  30  miles 
per  hr.,  has  a  normal  train  resistance  of  approximately  12.5 
Ib.  per  ton.  The  output  in  watt-hours  per  ton-mile  is  then  about 
25.  This  value  would  also  correspond  to  a  60-ton  car  at  35  miles 
per  hr.,  or  a  30-ton  car  at  20  miles  per  hr.  The  corresponding 
input  to  the  train  depends  on  the  efficiency  of  the  motors  and 
control.  If  the  average  efficiency  is  85  per  cent,  the  input  will 
be  29.4  watt-hours  per  ton-mile  for  this  particular  case. 

Effect  of  Length  of  Run  on  Energy. — If  it  is  necessary  to  limit 
the  length  of  run,  as  is  required  in  all  practical  operation,  addi- 
tional energy  must  be  supplied  beside  that  for  overcoming  train 
resistance.  The  amount  expended  in  accelerating  a  train  can 
be  found  at  once,  since  it  is  stored  in  the  kinetic  energy  of  the 
train,  and  is  numerically  equal  to  ^Mv2,  in  foot-pounds.  If 
the  50-ton  car  referred  to  in  the  preceding  paragraph  is  brought 
up  to  a  speed  of  60  miles  per  hr.,  the  energy  imparted  to  it  is 

(60X1.467). 

=  12,000,000  ft.-lb. 

=  12,000,000  X  0.0003766  =  4520  watt-hr. 

This  represents  the  stored  energy,  which  must  be  imparted  to 
the  train,  neglecting  the  energy  of  the  rotating  parts.  With  the 
ordinary  types  of  direct-current  control  the  efficiency  of  the 
electrical  equipment  will  not  be  more  than  about  55  per  cent, 
during  the  acceleration  period,  so  that  the  input  to  the  car  is 

4520 


0.55 


8230  watt-hr. 


The  efficiency  of  the  generating  and  substation  equipment, 
and  of  the  transmission  and  contact  lines,  during  the  period  of 
heavy  load  while  accelerating,  will  not  be  over  82  per  cent.,  so 
that  the  total  electrical  input  represented  is  approximately  10,000 
watt-hr.  at  the  switchboard.  At  the  lowest  cost  of  energy,  0.5 
ct.  per  kw.-hr.,  this  will  amount  to  5  cts.,  which  is  about 
the  cost  for  stopping  a  limited  interurban  car.  In  sparsely  settled 
territory,  where  a  train  may  be  required  to  make  two  separate 
stops  for  a  single  passenger,  a  10-ct.  fare  will  just  pay  for  the 
cost  of  stopping  the  train. 


154  THE  ELECTRIC  RAILWAY 

A  portion  of  the  kinetic  energy  may  be  recovered  if  the  train 
is  allowed  to  coast  before  the  brakes  are  applied  in  making  a 
stop.  In  this  way  the  energy  may  be  returned  in  overcoming 
train  resistance.  It  must  be  remembered  that  one-half  the  total 
kinetic  energy  will  have  been  removed  when  the  train  has  had 
its  speed  reduced  to  0.7  of  the  maximum.  For  instance,  the 
train  in  the  last  example  will  have  given  up  6,000,000  ft.-lb.  if 
it  has  been  allowed  to  coast  down  to  a  speed  of  42  miles  per  hr. 

The  effect  of  stops  on  the  energy  consumption  per  ton-mile 
can  be  determined  if  the  number  of  stops  per  mile  is  known.  If 
the  50-ton  car  is  running  on  a  schedule  which  calls  for  one  stop 
per  mile,1  the  total  energy  will  be  that  for  train  resistance  already 
found,  plus  that  for  acceleration.  This  latter  would  be 

12,000,000 


50 

4520 
50 


=  240,000    ft.-lb.   per   ton-mile,  or 


=  90  watt-hr.  per  ton-mile. 


The  total  output  of  the  motors  for  such  a  run  is  therefore  90  + 
25  =  115  watt-hr.  per  ton-mile.  If  the  same  maximum  speed 
is  attained,  and  the  length  of  run  is  5  miles,  the  total  output  of 
the  motors  is  18  +  25  =  43  watt-hr.  per  ton-mile.  The  corre- 
sponding inputs  may  be  determined  if  the  efficiency  of  the 
equipment  is  known.  Assuming  the  same  values  for  efficiency 
as  before,  the  inputs  to  the  car  would  be  193.4  and  62.1  watt-hr. 
per  ton-mile,  respectively,  for  the  1-mile  and  the  5-mile  runs. 
The  effect  of  frequent  stops  is  thus  seen  to  increase  the  energy 
by  a  marked  amount  when  the  maximum  speed  is  high.  For 
this  reason  the  speed  attained  should  be  held  to  as  low  a  value  as 
possible,  consistent  with  the  required  schedule  speed.  This  may 
be  done  by  the  use  of  high  acceleration  and  retardation.  It  is 
especially  important  on  city  lines,  where  the  stops  will  average 
from  four  to  ten  per  mile.  High-speed  operation  under  such 
conditions  calls  for  an  energy  consumption  out  of  all  propor- 
tion to  the  value  of  the  service  rendered. 

Another  effect  of  stops  is  to  increase  the  running  time,  or, 
conversely,  to  reduce  the  schedule  speed.  With  ordinary  inter- 
urban  cars,  and  the  usual  schedule  speed,  rates  of  acceleration 
and  braking,  the  effect  of  a  single  stop  is  to  add  about  one  minute 
to  the  running  time.  This  is  in  addition  to  the  time  actually 

1  Such  a  schedule  is  manifestly  impossible,  but  the  value  of  the  com- 
parison is  not  changed  thereby. 


ENERGY  CONSUMPTION  155 

consumed  in  the  stop,  which  may  vary  from  a  few  seconds 
to  several  minutes. 

.  It  will  be  noted  that  the  maximum  speed  attained,  rather  than 
the  schedule  speed,  has  an  effect  on  energy  consumption.  If,  by 
means  of  rapid  acceleration  and  braking,  the  maximum  is 
maintained  for  a  large  portion  of  the  run,  the  schedule  speed  will 
be  raised  without  a  great  increase  in  energy  consumption.  This 
is  very  marked  in  the  shorter  runs,  and  less  so  in  the  long  ones. 
This  is  another  argument  for  high  rates  of  acceleration  in  city 
service.  Since  the  schedule  speed  more  nearly  approaches  the 
maximum,  the  greater  the  acceleration  and  retardation,  the 
maximum  speed  required  to  give  a  certain  schedule  speed  may 
be  reduced;  and  the  energy  input  is  lowered  in  proportion  to  the 
square  of  the  maximum  speed. 

Influence  of  Grades  on  Energy. — Since,  in  a  complete  round 
trip,  a  car  must  go  up  and  down  all  the  grades  on  the  line,  the 
net  effect  of  them  on  the  energy  consumption  is  nil,  if  the  brakes 
do  not  have  to  be  applied  to  keep  the  train  from  reaching  too 
high  a  speed.  As  many  grades  do  require  brake  applications 
to  prevent  the  attainment  of  dangerous  velocities,  there  will  be, 
in  general,  some  increase  of  energy  consumption  if  the  grades 
are  at  all  steep.  The  exact  value  can  only  be  determined  by 
an  analysis  of  any  particular  problem. 

In  trunk  line  work,  especially  with  heavy  freight  trains, 
the  energy  consumption  will  be  increased  to  a  marked  degree 
if  numerous  grades  are  encountered.  In  the  operation  of  freight 
trains,  the  maximum  speeds  are  comparatively  low,  and  the 
train  resistance  much  less  than  in  passenger  service.  On  account 
of  the  large  mass  of  freight  trains,  a  large  force  is  required  for 
overcoming  an  opposing  grade;  and,  to  ensure  safe  operation, 
braking  must  be  resorted  to  even  on  comparatively  slight 
declines. 

There  is  one  case  where  the  grades  can  actually  be  used  to  ad- 
vantage in  the  propulsion  of  trains.  If  a  down  grade  exists  out 
of  a  station,  the  force  of  the  grade  will  aid  the  motive  power 
in  accelerating  the  train;  and,  for  trains  coming  into  the  station 
in  the  opposite  direction,  the  same  grade  will  help  retard  them. 
Such  a  grade  is  a  positive  benefit,  provided  all  trains  are  re- 
quired to  stop  at  this  point.  If  each  main  station  can  be  located 
at  the  crest  of  a  hill,  the  assistance  of  the  grade  can  be  had  in 
both  directions,  and  may  even  result  in  reducing  the  size  of  the 


156 


THE  ELECTRIC  RAILWAY 


motive  power  required.  For  through  trains,  which  do  not  stop 
at  the  stations,  the  only  result  is  to  add  a  certain  amount  of 
rise-and-fall  to  the  line,  which  will  have  a  relatively  small  effect 
in  train  operation. 

In  general,  it  is  not  possible  to  place  all  stations  so  as  to  make 
use  of  this  phenomenon.  In  the  case  of  elevated  track  through 
cities  it  can  be  done  without  any  greatly  increased  expense. 
In  elevated  or  underground  railroads,  the  construction  of  the 
line  with  such  grades  is  entirely  feasible;  and  some  roads  have 
been  built  with  the  stations  elevated  above  the  general  contour 
of  the  road. 


1.0 


as   400  40 


0.6     300     30 


(MgZOO^ZO 


02     100      10 


60  80 

Seconds 

FIG.  80. — Distribution  of  energy  consumption. 

Showing  the  distribution  of  the  energy  input  to  a  50-ton  car  when  making  a  1-mile  run. 
The  sum  of  all  the  losses  is  just  equal  to  the  total  energy  input  to  the  car. 

Distribution  of  Energy  Input. — After  having  taken  up  in  detail 
the  elements  of  the  energy  needed  for  train  propulsion,  it  is 
interesting  to  see  the  distribution  of  the  input.  In  Fig.  80  is 
shown  the  distribution  of  the  energy  for  propelling  a  certain 
car  over  a  run.  Of  the  total  amount  supplied  from  the  dis- 
tributing circuit,  a  portion  is  lost  in  the  wiring.  During  the 
operation  of  the  controller,  some  of  the  energy  is  converted  into 
heat  in  the  resistance.  Of  the  motor  input,  a  portion  supplies 
the  electrical  losses,  and  another  part  the  mechanical  losses  in 
gears  and  bearings.  The  remainder  is  used  for  the  propulsion 
of  the  train.  Of  this  output,  a  certain  amount  is  used  to  over- 
come train  resistance,  the  balance  being  converted  into  kinetic 
energy,  which  is  partly  used  to  supply  the  train  resistance  while 


ENERGY  CONSUMPTION  157 

coasting,  the  residue  being  absorbed  in  the  brakes.  The  rela- 
tions of  the  different  uses  of  the  input  are  clearly  shown  in  the 
diagram. 

Energy  for  Auxiliaries. — In  addition  to  the  energy  used  directly 
in  the  propulsion  of  trains,  there  is  in  most  cases  a  demand  for 
an  additional  amount  in  auxiliary  circuits  on  the  train. 

Practically  all  electric  cars,  except  the  smallest  single-truck 
city  cars,  are  equipped  with  air  brakes,  the  air  being  compressed 
by  a  pump  on  each  motor  car,  driven  by  an  electric  motor.  The 
requirements  of  this  circuit,  while  small,  must  be  added  to  the 
power  demands;  and,  since  the  pump  runs  a  considerable  portion 
of  the  time,  the  amount  of  energy  is  worth  taking  into  account. 
Tests1  have  shown  that  the  energy  for  operating  the  air  brakes 
in  city  service  is  from  1  per  cent,  to  2  per  cent,  of  that  required 
for  the  traction  motors.  In  inter  urban  service  the  energy  for 
braking  is  from  5  to  12  watt-hr.  per  stop  for  a  40-ton  car,  depend- 
ing on  the  rate  of  retardation.  It  is  worth  noting  that  on  cars  pro- 
vided with  air  whistles,  the  energy  used  in  this  service  is  about 
equal  to  that  for  braking,  unless  special  care  is  taken  to  prevent 
excessive  use  of  the  whistle.  This  has  the  effect  of  overloading 
the  compressor.  In  cars  equipped  with  electropneumatic 
control,  there  is  additional  compressed  air  needed.  The  amount 
for  this  is  so  small  as  to  be  of  little  consequence.  On  many  rapid- 
transit  lines,  door-operating  mechanisms  are  worked  with  com- 
pressed air.  This  makes  a  considerable  addition  to  the  other 
uses,  and  must  be  allowed  for.  Other  pneumatically  operated 
devices  have  been  introduced  which  call  for  additional  energy, 
so  that  the  total  required  for  these  auxiliaries  may  amount  to 
several  per  cent,  of  the  total. 

Practically  all  electric  cars  are  lighted  from  the  trolley  circuit. 
The  demand  for  energy  can  be  readily  calculated.  Although  it 
is  not  large  for  a  single  car,  it  makes  a  considerable  total  for  a 
city  system.  The  older  forms  of  lighting  almost  invariably  con- 
sist of  16-c.p.  carbon  lamps,  consuming  approximately  55  watts, 
and  connected  in  series  of  five  on  the  trolley  circuit.  The  number 
of  lamps  per  car  varies  from  five  to  twenty-five,  depending  on 
the  size  of  the  car  and  the  individual  taste  of  the  designer.  In 
more  recent  equipments  tungsten  lamps  have  been  used  to  ad- 
vantage to  reduce  the  energy  consumption,  cutting  it  down  in 

1  Report  of  the  Electric  Railway  Test  Commission,  McGraw  Publishing  Co., 
1906. 


158  THE  ELECTRIC  RAILWAY 

extreme  cases  from  1.5  kw.  to  0.5  kw.,  and  at  the  same  time 
giving  better  lighting. 

Heating  of  city  cars  is  most  frequently  done  with  electric 
power.  The  amount  of  energy  required  to  keep  the  temperature 
to  a  reasonable  point  on  cold  days  is  quite  considerable,  a  test 
on  a  large  city  road1  showing  a  power  consumption  of  3.3  kw. 
at  full  load  on  the  heaters,  or  16  per  cent,  of  the  total  power  taken 
by  the  car.  In  elevated  service,  under  similar  conditions,  the 
power  for  heating  was  8.25  kw.  or  18  per  cent,  of  the  total. 

For  high-speed  interurban  roads  the  demands  for  heating  are 
much  greater,  so  that  in  many  cases  heaters  taking  energy  direct 
from  coal  are  used  on  account  of  their  lower  operating  cost.  This 
is  discussed  more  fully  in  Chapter  VIII. 

Regeneration  of  Electric  Energy. — It  has  been  shown  that  of 
the  total  input  for  train  operation,  a  large  portion  is  used  to  pro- 
duce kinetic  energy.  In  case  grades  are  encountered,  another 
portion  of  the  input  will  be  converted  into  potential  energy. 
While  these  forms  readily  admit  of  reconversion  into  some  other, 
they  are,  in  general,  not  utilized,  since  it  is  necessary  to  destroy 
the  energy  of  the  train  by  means  of  brakes  in  order  to  prevent  too 
high  a  speed,  or  to  bring  the  train  to  rest.  If  this  energy  could 
be  recovered  in  some  useful  form,  the  total  requirement  would  be 
that  needed  to  overcome  train  resistance  alone,  with  an  addition 
for  the  inevitable  losses  in  the  electric  circuit. 

Many  attempts  have  been  made  to  recover  an  appreciable 
amount  of  this  energy  and  return  it  to  the  electric  circuit. 
Generally  speaking,  all  of  the  proposed  methods  include  the  use 
of  the  motors  as  electric  generators.  To  get  a  motor  which  will 
deliver  energy  to  the  line  requires  that  the  magnetic  flux  be  to  a 
large  extent  independent  of  the  load.  In  direct-current  practice, 
a  motor  with  shunt  characteristics  is  necessary,  and  in  alternat- 
ing-current service  a  shunt  characteristic  must  be  obtained,  or 
the  motor  must  be  of  the  induction  type.  None  of  the  motors 
which  have  been  most  successful  in  railway  service  (i.e.,  series 
motors)  lend  themselves  readily  to  the  generation  of  current.  A 
glance  at  the  curves  of  a  series  railway  motor  (see  Fig.  19)  shows 
that  a  current  will  be  taken,  no  matter  how  high  a  speed  is  reached. 
This  is  true  whether  the  series  motor  is  operated  on  direct  current 
or  on  alternating  current.  The  shunt  motor  is,  however,  well 

1  HERRICK  AND  BOYNTON,  "  American  Electric  Railway  Practice,"  McGraw- 
Hill  Book  Co.,  Inc.,  1907. 


ENERGY  CONSUMPTION 


159 


adapted  for  this  service.  In  Fig.  81  the  curves  of  the  shunt  motor 
have  been  extended  beyond  the  origin  to  show  the  characteristic 
performance  under  a  wide  range  of  conditions.  If  the  speed  of 
the  motor  is  increased  beyond  the  normal  no-load  speed,  the 
current  in  the  armature  will  reverse,  and  the  machine  will  become 
a  generator,  returning  current  to  the  distributing  circuit.  If  the 
railway  system  is  at  all  extensive,  the  current  thus  fed  back  into 
the  line  can  be  used  for  the  propulsion  of  other  cars,  and  will 
reduce  the  load  on  the  generating  station.  The  proper  condition 
for  feeding  back  into  the  line  is  reached  whenever  the  motor  speed 
exceeds  the  no-load  speed.  In  other  words,  when  the  train  is 


1200  f 


Generator 


Motor 


800 


"8400 

8. 


400 


1200 


300          200          100  0  100          200 

Current j  Amperes 


300 


FIG.  81. — Shunt  motor  characteristics. 

The  performance  curves  of  the  shunt  motor,  Fig.  15,  are  re-drawn  to  show  the  performance 
fhen  the  speed  exceeds  the  normal  no-load  speed  of  the  machine. 


going  down  a  hill  on  which  the  tractive  effort  due  to  the  grade  is 
greater  than  the  train  resistance,  the  armature  current  will  re- 
verse without  any  change  in  the  motor  connections.  Regenera- 
tion is  thus  entirely  automatic. 

With  the  induction  motor,  the  performance  is  almost  precisely 
the  same  as  with  the  direct-current  shunt  motor.  In  neither  case, 
however,  is  the  motor  inherently  suited  to  give  the  large  tractive 
effort  required  for  starting  with  a  high  acceleration.  For  this 
reason  motors  of  the  constant-speed  type  have  never  become 


160 


THE  ELECTRIC  RAILWAY 


popular  for  traction.     In  a  hilly   country,  however,  the  value 
of  the  energy  saved  may  overbalance  the  disadvantages. 

When  motors  of  the  series  type  are  to  be  employed  for  re- 
generation, it  is  necessary  to  modify  their  characteristics  by  the 
addition  of  a  shunt  winding,  or  by  a  reconnection  of  the  series 
fields  to  the  line,  as  in  Fig.  82.  This  gives  them  performance 
curves  like  those  shown  in  Fig.  81,  and  the  operation  is  the  same 
as  that  of  the  shunt  machine.  In  this  case  it  is  necessary  to  pro- 
vide proper  controller  connections  for  making  the  desired  changes 
as  needed.  For  small  equipments  the  complication  introduced 
in  the  control,  and  the  addition  of  an  extra  winding,  have 
prevented  the  adoption  of  this  feature. 


Armatures 


Fields 


FIG.  82. — Arrangement  of  series  motors  for  regeneration. 
The  fields  are  placed  in  series  with  a  suitable  resistance,  while  the  armatures  are  connected 
in  parallel  across  the  line. 

In  order  to  return  a  portion  of  the  energy  of  acceleration,  it  is 
further  necessary  to  change  the  characteristics  of  the  motor  in 
such  a  manner  that  it  will  generate  in  spite  of  a  reduction  in  speed. 
In  the  shunt  machine,  this  may  be  done  if  the  field  strength  be 
made  considerably  greater.  By  increasing  the  flux  the  normal 
speed  is  reduced,  so  that  if  this  change  is  suddenly  made  the  motor 
will  then  be  operating  above  its  new  no-load  speed,  and  energy 
will  be  returned  until  the  speed  corresponding  to  the  particular 
field  strength  has  been  reached.  The  range  through  which  this 
can  be  accomplished  may  be  further  increased  if  two  or  more 
armatures  are  put  in  series  as  the  train  speed  becomes  less.  With 


ENERGY  CONSUMPTION  161 

induction  motors  the  same  result  can  be  had  by  concatenation, 
or  by  changing  the  number  of  poles.  The  range  of  speed  over 
which  energy  can  be  regenerated  is  of  course  limited  in  any  type 
of  motor;  but  it  must  be  remembered  that  the  larger  part  of  the 
energy  can  be  returned  by  a  comparatively  small  speed  reduction. 
For  instance,  if  induction  motors  are  employed,  and  the  speed 
is  reduced  to  one-half  by  concatenation,  the  amount  of  energy 
returned  is  three-fourths  of  the  total  kinetic  energy  at  full  speed. 

It  must  not  be  taken  for  granted  that  the  entire  amount  of 
stored  energy  can  be  returned  to  the  electric  system  and  used  at 
some  other  point.  The  inevitable  losses  in  the  machines  and  in 
the  electric  circuits  will  reduce  the  quantity  available  by  a  con- 
siderable degree.  The  net  amount  of  energy  which  can  be  re- 
turned may  be  quite  large  in  certain  classes  of  service.  On 
mountain  roads,  for  instance,  where  braking  is  ordinarily  used 
to  prevent  an  excessive  speed,  the  energy  which  can  be  recovered 
may  amount  to  a  material  proportion  of  the  entire  demand.  In 
such  a  case  the  necessary  complication  of  the  motors  and  control 
may  be  well  worth  while. 

Effects  of  Regeneration  on  Equipment. — The  use  of  the  trac- 
tion motors  for  the  return  of  energy  to  the  line  cannot  be  done 
without  a  definite  increase  in  the  heating.  The  motors  are  work- 
ing for  a  larger  portion  of  the  total  time,  so  that  both  the  r.m.s. 
current  and  the  average  motor  potential  are  higher;  this  results 
in  greater  copper  and  iron  losses,  with  increase  in  the  average 
motor  load.  If  the  motors  are  only  of  sufficient  continuous 
capacity  to  propel  the  cars  in  the  usual  manner,  the  addition  of 
the  regeneration  feature  will  cause  them  to  be  loaded  beyond  their 
normal  rating,  and  hence  to  overheat. 

In  many  cases  the  motors  will  have  sufficient  reserve  capacity, 
so  that  the  addition  of  regeneration  will  still  keep  the  load  within 
the  rating  of  the  motors,  in  which  event  no  change  is  necessary. 
Each  case  must  be  considered  separately,  the  values  of  r.m.s. 
current  and  average  motor  potential  being  determined  by  the 
method  already  given. 

Another  result  of  the  regeneration  of  energy  is  the  reduction 
in  brake-shoe  friction  needed  in  controlling  the  speed  of  the  train. 
Since  in  ordinary  operation  the  energy  of  the  train  is  absorbed 
by  the  brake  shoes,  with  consequent  production  of  heat,  there 
will  be  a  considerable  amount  of  brake-shoe  wear  caused  by  the 
friction.  The  use  of  regeneration  removes  a  large  amount  of 
11 


162  THE  ELECTRIC  RAILWAY 

work  from  the  brakes,  so  that  the  shoe  wear  is  materially  re- 
duced, resulting  in  a  saving  of  cost  in  brake  shoes  and  wheels. 
The  wheels  are  also  subject  to  various  troubles  from  overheating. 
In  general,  the  wheels  of  American  freight  cars  are  of  cast  iron, 
with  the  treads  chilled  to  resist  wear.  The  alternate  heating  and 
cooling  due  to  braking  sometimes  cause  annealing  of  the  chill, 
with  resultant  increased  wear.  In  extreme  cases  the  metal 
is  likely  to  crack  or  "  shell  out,"  necessitating  the  removal  of 
the  affected  wheel  from  service,  perhaps  long  before  it  has 
reached  the  normal  limit  of  life.  A  large  portion  of  this  wear 
can  be  prevented  by  regeneration,  which  will  also  relieve  other 
parts  of  the  equipment,  such  as  the  brake  rigging,  and  will  re- 
duce the  load  on  the  air  compressors  and  other  parts  of  the 
braking  system.  Such  advantages  as  these  may  be  worth  more 
than  the  actual  return  of  energy. 

A  possibility  exists  in  connection  with  the  use  of  direct-current 
shunt  motors  for  regeneration.  If  a  shunt  motor  be  made  with 
a  maximum  strength  of  field  at  least  equal  to  the  greatest  avail- 
able field  on  a  series  motor  of  the  same  rating,  it  will  give  equal 
or  greater  torque  with  the  same  armature  current.  It  can 
accelerate  up  to  the  normal  operating  speed,  which  will  be 
approximately  the  same  as  that  of  the  series  motor  at  maximum 
current.  For  acceleration  above  this  point,  the  strength  of 
field  can  be  reduced  by  the  insertion  of  resistance  in  series  with 
the  shunt  field  winding.  Proper  proportioning  of  the  resistance 
will  allow  the  motor  to  produce  an  acceleration  curve  approxi- 
mately the  same  as  that  for  a  series  motor  of  equal  capacity. 
A  motor  of  this  type  will  have  the  advantage  over  the  series  motor 
that  any  speed  above  that  with  the  maximum  field  strength  is 
an  operating  one;  and  all  the  operating  speeds  will  give  practically 
maximum  efficiency.  The  same  motor  can  be  used  for  slow- 
speed  work,  with  rapid  acceleration,  on  city  streets,  or  for  high- 
speed work  on  private  right-of-way.  Regeneration  on  down 
grades  can  be  accomplished  at  any  desired  operating  speed  by 
proper  adjustment  of  the  field  resistance.  To  return  energy  to 
the  line  when  stopping,  the  field  strength  can  be  increased  by 
cutting  out  resistance,  thus  increasing  the  counter  e.m.f.  of  the 
motor  until  energy  is  recovered.  The  motor  armatures  can 
be  connected  in  series  to  carry  the  regeneration  still  further. 

The  principal  objection  to  this  type  of  motor  and  control 
appears  to  be  the  lack  of  safeguard  against  overload.  With 


ENERGY  CONSUMPTION  163 

the  series  machine,  an  increase  in  load  is  accompanied  by  corre- 
spondingly greater  field  strength,  thus  automatically  reducing 
the  speed  and  limiting  the  overload.  With  the  shunt  motor  no 
such  inherent  safety  device  is  present,  the  field  strength  remaining 
constant  unless  varied  independently.  It  is  possible,  however, 
to  introduce  a  relay  which  will  automatically  increase  the  field 
current  when  an  overload  occurs,  thus  giving  the  same  form  of 
protection  as  in  the  series  motor.  Although  this  method  of 
operation  has  never  been  tried,  it  has  very  attractive  possi- 
bilities, and  may  in  the  future  be  extensively  used,  both  for 
interurban  and  trunk-line  service. 


CHAPTER  VII 
BRAKING  OF  ELECTRIC  RAILWAY  TRAINS 

Importance. — Even  though  it  is  of  importance  to  get  a  train 
in  motion  rapidly,  it  is  none  the  less  essential  to  be  able  to  arrest 
its  movement  when  desired,  at  a  rate  comparable  with  the  ac- 
celeration, and  in  such  a  manner  that  the  action  may  be  pre- 
determined with  a  considerable  degree  of  accuracy.  Indeed, 
from  the  standpoint  of  safety,  the  braking  of  trains  is  of  even 
greater  importance  than  their  acceleration. 

It  is  shown  in  the  previous  chapter  that  a  high  rate  of  ac- 
celeration is  required  to  reduce  the  amount  of  energy  consumed. 
It  is  equally  true  that  a  rapid  retardation  is  desirable  to  cut 
down  the  running  time  between  stops.  It  must  be  noted,  how- 
ever, that  one  of  the  economies  effected  by  the  rapid  retardation 
is  due  to  the  fact  that  the  train  is  able  to  propel  itself  for  a  portion 
of  the  distance  by  its  own  momentum,  for  the  rapid  reduction  of 
speed  produced  in  braking  by  ordinary  methods  converts  a  large 
portion  of  the  stored  energy  into  heat  without  performing  any 
useful  work.  Granted  that  the  most  efficient  run  is  the  one  where 
the  brakes  are  applied  at  the  lowest  practicable  speed,  the  retard- 
ation from  this  point  should  be  the  highest  allowable,  since  the 
added  distance  covered  when  a  lower  rate  of  braking  is  used  is 
more  than  offset  by  the  decreased  average  speed  at  which  this 
part  of  the  run  is  made. 

Methods  Available  for  Retardation. — Since  it  is  universally 
granted  that  some  form  of  braking,  by  means  of  which  the 
speed  of  a  train  may  be  reduced  at  a  rapid  rate,  is  a  necessity, 
the  next  thing  is  to  determine  what  forces  may  be  employed  to 
effect  this  retardation,  and  what  methods  may  be  used  to  make 
them  available. 

One  force  is  always  present,  and  is  universally  applicable  in 
decreasing  the  velocity.  This  is  the  train  resistance.  Since  it 
increases  with  the  speed,  it  is  greatest  when  it  is  most  needed. 
If  curvature  of  the  track  is  present,  it  will  also  aid  in  retardation. 
Grades  may  assist,  or  may  hinder,  depending  on  the  direction  of 

164 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     165 

motion.  The  train  resistance,  even  in  favorable  cases,  is  not 
sufficient  to  control  the  train  motion  satisfactorily.  The  force 
due  to  this,  acting  on  a  single  50-ton  car  at  a  speed  of  60  miles 
per  hr.,  is  about  27  lb.  per  ton,  which  will  produce  a  retardation 
of  approximately  0.27  miles  per  hr.  per  sec.,  which  is  entirely 
inadequate  for  practical  operation,  since,  if  the  force  remained 
the  same  until  the  train  were  brought  to  rest,  a  time  of 
221  seconds  would  be  necessary  to  stop  the  car.  It  is  evident 
that  some  additional  force  is  required. 

The  most  obvious  method  of  obtaining  an  additional  retarding 
force  is  to  produce  friction  against  the  track.  This  has  been  used 
in  some  cases.  On  a  few  gravity  roads  dogs  are  employed  which 
engage  the  ties,  so  that  if  the  car  stops  on  the  up-grade,  the  dogs 
will  act  and  prevent  the  car  from  running  backward  down  the 
track.  A  more  refined  method  of  producing  friction  against  the 
track  is  to  use  metallic  blocks  which  may  be  pressed  on  the  rails. 
This  has  been  employed  in  connection  with  certain  of  the  cable 
roads  which  were  popular  at  one  time.  This  method  of  retarda- 
tion is  poor,  since,  as  will  be  seen,  the  sliding  friction  obtainable 
between  the  brake  blocks  and  the  rails  is  less  than  that  which 
can  be  obtained  by  other  means. 

The  other  available  method  of  utilizing  friction  as  a  retarding 
force  is  to  produce  the  friction  by  the  pressure  of  blocks  against 
the  car  wheels.  When  this  is  done,  it  is  essential  that  the  wheels 
have  sufficient  adhesion  on  the  rails  to  prevent  sliding,  or  the 
conditions  would  be  the  same  as  with  the  track  brake  already 
described;  and  the  rubbing  of  a  single  place  on  a  wheel  against 
the  rail  would  result  in  wearing  a  flat  spot  on  the  locked  wheel, 
which  would  hinder  its  further  operation. 

The  first  railway  cars  were  readily  brought  to  rest  by  means  of 
force  applied  to  wooden  blocks  bearing  against  the  wheels.  This 
natural  solution  of  the  problem  needed  modification  for  heavier 
equipment  only  by  increasing  the  pressure  of  the  brake  shoes,  and 
the  use  of  a  material  which  would  resist  wear  while  giving  suffi- 
cient friction  to  be  effective.  The  force  was  applied  to  the  shoes 
by  means  of  a  system  of  levers  operated  by  hand.  This  type  of 
brake  has  been  used  to  a  very  great  extent  for  all  classes  of 
vehicles.  It  was  the  only  kind  employed  on  steam  railway  cars 
for  many  years,  and  is  today  retained  as  a  valued  auxiliary. 

Need  for  Power  Brakes. — Although  the  hand  brake,  as  just 
described,  was  adequate  for  the  light  cars  and  low  speeds  in  com- 


166  THE  ELECTRIC  RAILWAY 

mon  use  25  years  ago,  its  limitations  have  been  exceeded  in  nearly 
every  form  of  railway  vehicle.  Except  in  the  case  of  slow-speed 
city  cars  of  light  weight,  some  form  of  brake  applied  by  a  power 
more  certain  and  of  greater  amount  than  the  available  muscular 
force  of  the  operator,  must  be  employed.  It  should  be  re- 
membered that  a  large  share  of  the  kinetic  energy  of  the  moving 
train  must  be  absorbed  by  the  brakes,  only  a  small  portion  of  it 
being  taken  care  of  by  the  train  resistance.  Since  the  kinetic 
energy  increases  directly  as  the  weight  and  as  the  square  of  the 
speed,  it  may  be  seen  that  the  stopping  of  a  20-ton  car  from  a  speed 
of  20  miles  per  hr.  will  require  the  absorption  of  eight  times  the 
energy  possessed  by  a  10-ton  car  running  at  10  miles  per  hr. 
While  the  hand  brake  will  take  care  of  the  latter  case  with  ease, 
the  former  is  practically  beyond  its  range  of  efficient  operation. 
As  20  tons  is  about  the  minimum  weight  of  car  now  in  use,  ex- 
cept for  very  light  city  service,  the  application  of  power  brakes 
to  all  electric  cars  has  been  agitated  in  many  quarters.  A  study 
•of  the  different  forms  of  power  brakes  available  is  therefore 
pertinent. 

Nature  of  Braking  Phenomena. — All  the  mechanical  relations 
in  braking  follow  the  laws  of  motion.  These  laws  have  already 
been  discussed  in  some  detail  in  Chapter  II.  Retardation  is  a 
phenomenon  of  a  character  precisely  similar  to  acceleration,  and 
may  be  correctly  regarded  as  negative  acceleration.  It  will  not 
be  necessary  to  repeat  the  fundamental  relations;  but  it  is  well 
to  note  that,  retardation  being  opposed  to  the  direction  of  motion, 
the  algebraic  signs  of  the  functions  should  be  carefully  checked 
in  order  to  prevent  mistakes. 

Adhesion  Coefficient. — It  has  already  been  mentioned  that, 
in  order  to  utilize  friction  between  the  wheels  of  a  train  and  brake 
shoes  bearing  against  them,  the  force  applied  shall  not  be  so 
great  that  the  available  adhesion  between  the  wheels  and  the 
rail  shall  be  exceeded.  The  coefficient  of  sliding  friction  is  less 
than  that  of  rolling  friction  (or  adhesion).  If  sliding  takes  place 
the  maximum  braking  effort  which  can  be  obtained  will  be  re- 
duced. It  has  also  been  pointed  out  that  sliding  causes  undue 
wear  on  the  wheels. 

Although  the  values  of  adhesion  have  never  been  experi- 
mentally checked  through  a  wide  range  of  conditions,  the  follow- 
ing fairly  represent  the  result  of  such  tests  as  have  been  made : 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS    167 

COEFFICIENTS  OF  ADHESION  BETWEEN  DRIVERS  AND  RAIL1 


Normal 

With  sand 

Most  favorable  condition 

0  35 

0  40 

Clean  dry  rail  

0.28 

0.30 

Thoroughly  wet  rail  .         

0.18 

0  24 

"Greasy"  moist  rail 

0  15 

0  25 

Sleet-covered  rail 

0  15 

0  20 

Dry  -snow-covered  rail  

0.11 

0.15 

It  may  be  noted  from  the  above  table  that  the  normal  adhesion 
with  dry  rails  is  over  25  per  cent. ;  while  with  the  use  of  sand  the 
coefficient  need  not  fall  below  20  per  cent,  except  with  the  most 
unfavorable  conditions.  In  general,  a  maximum  force  equal  to 
about  one-quarter  the  train  weight  may  be  applied  at  the  wheel 
treads  either  for  acceleration  or  retardation,  without  slipping. 
If  all  of  this  force  were  availed  of  it  would  produce  an  ac- 
celeration amounting  to 

2000  X  0.25  X  0.01  =  5  miles  per  hr.  per  sec. 

This  includes  energy  of  rotation  equivalent  to  one-tenth  of  the 
linear  inertia.  This  extreme  value  of  acceleration  is  seldom 
reached  in  practice,  since  it  is  in  most  cases  far  beyond  the 
maximum  capacity  of  ordinary  motive  powers  or  brake  rigging. 
On  account  of  the  variable  character  of  the  adhesion  coefficient, 
it  would  be  unwise  to  attempt  to  design  braking  equipment  up 
to  this  limit.  In  most  cases,  accelerations  and  retardations  of 
from  1.5  to  2.0  miles  per  hr.  per  sec.  will  be  found  ample  for 
service  conditions,  although  greater  rates  are  demanded  for 
emergency  braking. 

It  may  be  noted  in  this  connection  that  the  adhesion  is  affected 
to  a  considerable  extent  by  the  area  of  the  contiguous  surfaces. 
It  is  usually  assumed  that  the  contact  between  wheel  and  rail  is 
a  line;  but,  since  both  are  compressed  to  some  extent,  the  con- 
tact really  is  a  surface.  The  shape  of  this  surface  varies  with  the 
elasticity  of  the  metal,  and  is  evidently  greater  with  large  di- 
ameter wheels  than  with  small  ones.  The  reduction  in  adhesion 
is  very  marked  in  locomotive  testing  plants,  where  the  drivers 
are  carried  directly  on  supporting  wheels  of  approximately  the 

XEDW.  P.  BURCH,  "Electric  Traction  for  Railway  Trains,"  p.  406,  Mc- 
Graw-Hill Book  Co.,  Inc.,  1911. 


168 


THE  ELECTRIC  RAILWAY 


same  size.     In  this  case  slipping  occurs  with  much  lower  values  of 
adhesion  than  on  ordinary  track. 

Sliding  Friction. — This  follows  a  quite  different  set  of  laws  from 
rolling  friction.  It  was  first  given  a  thorough  investigation  by 
George  Westinghouse  and  Sir  Douglas  Galton  in  a  series  of 
tests  made  on  the  London,  Brighton  and  South  Coast  Railway 
(England)  in  1878,  and  reported  by  Galton  to  the  (British) 
Institution  of  Mechanical  Engineers  in  April,  1879.  These  tests, 
known  as  the  " Galton- Westinghouse  test's,"  have  become  classic, 
and  summarize  practically  all  that  is  known  at  the  present  time 


30 


£     20 


20  40  60 

Speed, Miles,pec  flour 

FIG.  83. — Variation  in  friction  with  speed. 


100 


on  the  subject  of  sliding  friction.  They  were  made  on  cast-iron 
brake  shoes  bearing  on  steel-tired  wheels,  and  cover  a  wide 
range  of  conditions.  The  best  published  interpretation  of  these 
tests  is  that  made  by  Mr.  R.  A.  Parke  in  a  paper  presented  before 
the  American  Institute  of  Electrical  Engineers.1  He  finds  that 
the  average  coefficients  of  friction  for  different  speeds  may  be 
expressed  by  the  equation 

f  =  _      °-326  (1) 

J  "  1  +  0.035327 

1  R.  A.  PARKE,  Railroad  Car  Braking,  Transactions  A   I.  E.  E.,  Vol.  XX, 
p.  235. 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS      169 

where  V  is  the  speed  in  miles  per  hour,  and  /  the  coefficient  of 
sliding  friction.  For  maximum  observed  coefficients,  the  equa- 
tion is 

_  0.382 

J  "  1  +  0.02933  V 

The  graphs  of  these  equations  are  shown  in  Fig.  83.  The  points 
plotted  are  the  values  obtained  in  the  Westinghouse  tests.  It 
may  be  clearly  seen  that  the  coefficient  of  friction  falls  rapidly 
from  a  maximum  of  0.33  at  standstill  to  less  than  0.11  at  a  speed 
of  60  miles  per  hr.1  If  a  braking  system  were  designed  to 
utlize  the  total  adhesion  at  standstill,  the  same  pressures  would 
give  only  one-third  the  value  determined  in  the  preceding 
paragraph.  For  any  other  value  of  braking  effort  a  correspond- 
ing reduction  in  friction  with  speed  will  take  place. 

Effect  of  Distance  on  Sliding  Friction. — Further  experiments 
made  by  Captain  Galton  appear  to  show  that  the  coefficient  of 
friction  also  decreases  as  a  function  of  the  time  during  which 
the  rubbing  of  two  surfaces  continues.  The  results  of  these 
tests  have  been  interpreted  by  Mr.  Parke  to  indicate  that  there 
is  a  different  curve  corresponding  to  each  initial  coefficient  of 
friction,  and  that  these  curves  are  of  the  form 

1  +  hs 

-  r+~tsf 

where  /  is  the  initial  coefficient  of  friction,  corresponding  to  a 
particular  speed  and  pressure,  s  is  the  distance,  in  feet,  traveled 
while  the  rubbing  surfaces  are  in  contact,  /i  the  coefficient  of 
friction  after  any  elapsed  distance,  and  h  and  c  are  constants. 
Using  the  results  of  the  Galton  tests,  the  values  found  for  h 
and  c  cause  equation  (3)  to  become 

1  +  0.000472  s 
1  +  0.002390  s  ; 

The  graphs  of  this  equation,  for  various  initial  speeds  and  co- 
efficients of  friction,  are  shown  in  Fig.  84.  The  points  are  those 
found  by  Captain  Galton  at  the  corrresponding  speeds  as  desig- 
nated by  the  figures.  Later  experiments  would  indicate  that 
a  constant  friction  is  reached  much  sooner  than  would  be  derived 

1  More  recent  tests  made  by  the  Pennsylvania  Railroad  agree  in  general 
with  the  curve  of  maximum  values,  but  sufficient  points  were  not  obtained 
to  determine  accurately  its  form. 


170 


THE  ELECTRIC  RAILWAY 


by  the  above  equation,  and  that  a  value  considerably  greater 
than  that  found  above  is  correct.  The  reason  why  Gal  ton's 
results  are  low  may  be  because  of  the  short  distances  included  in 
the  tests;  none  of  them  was  for  a  greater  recorded  length  than  900 
ft.  The  points  on  the  curve  in  which  the  coefficient  is  rapidly 
falling  therefore  preponderate. 

It  is  unfortunate  that  no  completer  mathematical  utilization 
of  the  characteristic  reduction  of  friction  with  time  can  be  made. 
Although  it  exerts  a  marked  influence  on  the  amount  of  time 
needed  for  bringing  a  train  to  a  stop,  the  variation  of  conditions 
affects  the  decrease  to  such  an  extent  that  no  exact  rules  can  be 
formulated.  Since  the  grade  directly  adds  to,  or  subtracts  from, 
the  braking  force  applied,  it  must  change  the  rate  of  retarda- 


0.20 


0  200  400  600 

Distance  ,  Feet. 

FIG.  84. — Variation  of  friction  with  distance. 
The  small  numbers  beside  the  points  refer  to  the  speeds  at  which  the  tests  were  made. 

tion,  independently  of  the  coefficient  of  friction.  This  has  the 
effect  of  varying  the  time  of  rubbing  between  shoe  and  wheel 
corresponding  to  a  given  braking  force,  so  that  the  final  result  is 
to  change  the  relation  of  the  coefficient  of  friction  and  time  or 
distance.  The  indication  is  that  the  brakes  are  relatively  more 
efficient  on  an  up  grade,  and  less  so  on  a  down  grade. 

The  relation  between  the  coefficient  of  friction  and  the  braking 
pressure  is  quite  complicated,  but  tests  indicate  that  the  co- 
efficient varies  inversely  with  it. 

The  bad  results  of  sliding  the  wheels,  as  increasing  the  time 
or  distance  needed  to  bring  a  train  to  a  stop  may  be  seen  by  a 
comparison  of  the  values  of  rolling  friction  (adhesion)  and 
sliding  friction.  When  the  wheels  keep  their  grip  on  the  track, 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     111 

and  rotate,  the  maximum  braking  force  that  can  be  applied  is 
that  which  produces  a  frictional  resistance  just  below  the  total 
adhesion  of  the  wheel  on  the  rail.  By  the  use  of  sand,  this  can 
nearly  always  be  kept  over  a  value  of  0.2.  When  the  braking 
force  exceeds  the  limiting  value  of  adhesion,  the  resistance  at 
the  contact  of  wheel  and  rail  obeys  the  laws  of  sliding  friction; 
and  it  may  be  seen  that  even  for  moderate  speeds  the  retarding 
force  will  be  less.  For  example,  the  coefficient  of  sliding  fric- 
tion at  a  speed  of  20  miles  per  hr.  is  0.192,  which  is  less  than 
the  adhesion  mentioned  above;  and,  since  the  friction  becomes 
less  with  the  distance  of  application,  this  represents  a  maximum 
value  at  that  speed. 

Combined  Effect  of  Variations  in  Friction  Coefficient.— In 
determining  the  retardation  which  will  be  produced  by  the  appli- 
cation of  a  given  braking  force,  all  of  the  variables  which  enter 
must  be  taken  into  account.  The  initial  friction  which  is  ob- 
tained at  any  given  speed  can  be  found  with  considerable  accuracy. 
It  apparently  declines  for  a  certain  distance,  due  to  the  effect  of 
the  general  reduction  in  friction  with  time  of  application;  but, 
since  the  braking  force  is  simultaneously  lowering  the  speed,  the 
friction  has  a  tendency  to  become  greater.  As  the  train  moves 
forward,  the  increase  of  friction  with  the  lower  speed  will  over- 
balance the  reduction  due  to  the  time  the  brakes  have  been 
applied,  first  very  slowly,  and  then  more  rapidly,  until,  when 
the  speed  is  very  low,  the  friction  becomes  so  great  as  to  stop 
the  train  abruptly.  This  effect  on  passenger  car  braking  can 
be  noticed  at  any  time.  To  offset  this  final  increase  in  friction, 
it  is  customary  to  reduce  the  braking  force  as  the  train  nears  a 
stop. 

Determination  of  Correct  Retardation. — In  connection  with 
the  energy  consumption  of  electric  trains,  it  has  been  'seen  that 
in  general  the  most  economical  run  is  that  in  which  the  accelera- 
tion is  the  highest.  A  great  deal  of  careful  experimental  and 
theoretical  engineering  has  been  done  to  determine  how  high 
the  acceleration  may  be  carried;  and  the  values  in  use  today 
represent  the  maxima  that  can  be  .applied  for  various  classes 
of  service.  On  the  other  hand,  very  little  has  been  accomplished 
in  the  employment  of  high  braking  rates  in  practice.  Although 
brakes  are  usually  designed  to  give  a  very  high  retardation  for 
emergency  service,  the  regular  applications  use  lower  values 
than  those  of  the  corresponding  accelerations.  This  is  the  more 


172  THE  ELECTRIC  RAILWAY 

marked,  since  the  use  of  a  large  tractive  effort  calls  for  a  great 
expenditure  of  energy  during  the  whole  starting  period,  while 
a  high  braking  force  merely  takes  a  larger  volume  of  compressed 
air,  furnished  at  a  cost  very  much  less  than  that  of  the  energy 
for  starting.  In  other  words,  it  should  be  profitable  to  use 
regularly  for  service  stops,  braking  rates  which  are  as  high  or 
higher  than  the  corresponding  accelerations,  working  the  brak- 
ing apparatus  on  the  edge  of  the  emergency  application  for 
each  stop.  This  will  also  eliminate  the  personal  element  to  some 
extent,  and  allow  the  predetermination  of  train  performance  with 
greater  accuracy. 

Transmission  of  Braking  Forces. — In  the  use  of  the  friction 
between  wheels  and  brake  shoes  for  the  production  of  the  re- 
tarding force  in  train  braking,  it  is  necessary  to  have  an  adequate 
means  of  transmission  of  the  force  to  the  desired  points,  and 
to  be  able  to  control  it  in  amount.  Since  it  is  undesirable  to  slide 
the  wheels,  precautions  must  be  taken  to  prevent  this  in  any 
brake  application,  while  at  the  same  time  the  force  used  is  as 
near  the  allowable  limit  as  needed  for  adequate  braking.  To 
determine  what  this  maximum  force  can  be  requires  a  knowledge 
of  the  distribution  of  the  weight  of  the  car  on  its  supporting 
wheels.  It  might  be  assumed  that  the  weight  is  carried  uni- 
formly on  all  the  wheels ;  but,  due  to  the  moment  developed  by 
the  application  of  the  retarding  force  away  from  the  center 
of  gravity  of  the  car,  the  distribution  will  be  considerably  dif- 
ferent from  this  average  value. 

Since  the  adhesion  between  wheel  and  rail  is  ultimately  used 
as  the  basis  of  ordinary  braking  systems,  the  point  of  applica- 
tion of  the  force  is  about  as  far  removed  from  the  theoretically 
correct  position  as  possible.  If  the  car  is  of  the  single-truck 
type,  it  can  be  considered  as  a  single  moving  mass;  or  if  of  the 
double-truck  type,  of  three  distinct  masses,  the  car  body  and  the 
two  trucks. 

Distribution  of  Forces  on  the  Car.— Since  the  center  of  gravity 
is  above  the  point  of  application  of  the  braking  force,  there  is  a 
tendency  to  rotate  the  car  body  in  the  same  direction  as  that  of 
the  wheels.  This  rotation  is  prevented  by  the  production  of  a 
greater  supporting  force  at  the  front  end  (either  the  forward 
truck,  in  a  double-truck  car,  or  the  forward  wheels  in  a  single- 
truck  car)  sufficient  to  balance  the  turning  moment.  It  is  evi- 
dent that  the  total  pressure  of  all  the  wheels  on  the  track  must 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     173 

be  equal  to  the  total  weight  carried,  so  that  the  effect  of  rota- 
tion of  the  car  body  and  trucks  is  the  same  as  though  a  portion 
of  the  mass  were  actually  transferred  from  the  rear  to  the  forward 
wheels  or  truck.  The  pressure  of  the  forward  wheels  of  the 
leading  truck  will  be  the  greatest,  and  that  of  the  rear  wheels 
of  the  rear  truck  the  least.  Since  most  cars  must  be  ready  to 
operate  in  either  direction  with  equal  facility,  the  pressure  of 
the  brake  shoes  must  not  exceed  that  which  will  skid  the  wheels 
on  the  rear  axle  of  the  car.  In  ordinary  passenger  cars,  with 
maximum  rates  of  retardation,  the  pressure  on  the  rail,  for  the 
rear  pair  of  wheels,  is  less  than  85  per  cent,  of  the  normal  pressure 
at  standstill  or  at  constant  speed.  This  represents  the  limit 
of  the  braking  force  that  can  be  applied,  and  it  must  be  seen 
that  it  causes  a  considerable  reduction  from  the  maximum 


r ^ t \ ^ 

•!  \ 

FIG.  85. — Distribution  of  braking  forces  on  car  body. 

braking  effort  theoretically  possible  were  the  forces  properly 
adapted  to  the  individual  wheel  loads. 

In  order  to  determine  the  actual  forces,  it  is  necessary  to  con- 
sider the  reactions  existing  between  the  car  body  and  the  trucks, 
and  also  those  in  the  trucks  themselves.  In  this  way  it  is  possible 
to  compute  the  allowable  braking  forces  for  any  set  of  conditions.1 

The  body  of  a  car,  shown  in  Fig.  85,  is  considered  as  a  "free 
body,"  the  trucks  having  been  replaced  by  their  reactions  PI 
and  P2.  The  trucks  being  alike  and  the  braking  forces  on  each 
wheel  being  the  same,  the  horizontal  effort  of  the  retarding  force 
will  be  the  same  for  each  truck,  being  represented  by  H.  The 
car  weight,  Wi,  acts  vertically  downward  at  its  center  of  gravity, 

which  is,  in  ordinary  cases,  at  a  distance  ~,  or  midway  between  the 
two  supporting  trucks.  The  action  of  the  brakes  causes  the  car 

1  The  following  treatment  is  based  on  the  method  of  R.  A.  PARKE,  Railroad 
Car  Braking,  Transactions  A.  I.  E.  E.,  Vol.  XX,  p.  252  (1902). 


174  THE  ELECTRIC  RAILWAY 

as  a  whole  to  be  retarded  at  a  rate  a,  so  that  the  total  retarding 
force  is 


or 

"  -  w 

Also,  since  the  total  reaction  of  the  trucks  must  evidently  be  equal 
to  the  entire  weight  of  the  car, 

Pi  +  P2  -  W1  =  0  (3) 

Taking  moments  about  PI  we  have 


'2 

whence 


2  gl 

Substituting  the  value  of  PZ  in  equation  (3), 


A  comparison  of  equations  (5)  and  (6)  shows  that  the  normal 

W\ 
weight  -£-,  supported  by  each  truck,  has  been  changed  by  the 

removal  of  an  amount  -  —  ;  —  from  the  rear  and  its  transfer  to 

gi 

the  forward  truck. 

If  the  car  is  intended  for  operation  in  both  directions,  as  is 
usually  the  case,  the  determining  factor  is  the  pressure  allowable 
on  the  rear  truck,  and  a  consideration  of  that  will  be  equally 
applicable  to  the  other  when  the  motion  is  reversed.  For  cars 
designed  to  run  in  one  direction  only,  it  is  possible  to  modify  the 
braking  forces  to  apply  a  greater  pressure  to  the  shoes  on  the 
forward  truck.  In  that  case  a  similar  calculation  to  the  one  fol- 
lowing can  be  made  for  the  forward  truck,  the  relations  being 
identical. 

Distribution  of  Forces  on  the  Truck.  —  Considering  the  rear 
truck  as  a  free  body,  Fig.  86,  the  car  has  been  replaced  by  its 
pressure  P2,  the  track  by  the  reactions  Ri  and  Rz,  and  the  braking 
force  on  the  rails  by  the  reactions  TI  and  T2.  Since  each  pair 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     175 


of  wheels  must  rotate  as  a  single  unit,  being  rigidly  pressed  on  the 
same  axle,  the  forces  TI  and  T2  may  be  considered  as  combined 
for  their  respective  pairs  of  wheels.  The  truck  weight  W2  acts 
through  the  center  of  gravity  of  the  truck,  at  a  distance  d  above 
the  rail  and  midway  between  the  wheels. 

Taking  a  summation  of  the  vertical  forces,  we  have 

(7) 


(8) 


Ri  +  R2  -  W 
and  a  summation  of  the  horizontal  forces  gives 

T1  +  T2  -  H —  =  0 


r-^-JL 


FIG.  86. — Distribution  of  braking  forces  on  truck. 

Taking  moments  about  R\, 
W2b   .  P2b 


or 


2 

W2 


-  R2b  -  Hh-  - 


<! 


0 


,P*_Hh_  Wtad 
'   2   '       b  qb 


Substituting  the  value  of  R2  in  equation  (7), 

_W*,P*__  Hh      W2ad 

"1  r»      ~T"    o  Z.  ~l. 


(9) 
(10) 

(H) 


Replacing  H  and  P2  by  their  values  found  in  equations  (2) 
and  (5),  equations  (8),  (10)  and  (11)  become,  respectively, 

W,  +  2W2a 


R*  = 


W  i  +  2W  2 


rh 

2g    lb 


~\  _ 


(12) 
(13) 


176  THE  ELECTRIC  RAILWAY 


W,  +  2W2      W,a  rh      el  ,   W>ad 

~~~ 


4 

A  comparison  of  equations  (13)  and  (14)  shows  that  the 
result  of  applying  the  brakes  is  to  reduce  the  rail  pressure  on 

each  pair  of  wheels  of  the  rear  truck  by  an  amount  -^r   [equa- 

zgi 

tions  (5)  and  (6)];  and  has  also  transferred  from  the  rear  to  the 
forward  wheels  of  the  truck  an  amount  equal  to 

ahWi       adWz 

2gb  gb 

If  the  car  is  to  be  operated  only  in  one  direction,  the  values  of 
all  forces  may  be  determined  and  all  pressures  on  the  brake 
shoes  modified  accordingly.  Ordinarily  cars  must  be  suitable  for 
operation  in  either  direction;  in  which  case  the  maximum  pres- 

t  -      t     u    i  Wi  +  2W2  ^ 

sure  for  any  pair  of  wheels  must  be  reduced  from  -    —  j—   -  to 

the  value  given  in  equation  (13). 
Solving  equation  (12)  for  a  we  have 


Since  TFi  +  2TF2  is  the  total  weight  of  the  car  the  equations 
above  may  be  simplified  by  designating  by  W  the  total  weight,  or 

W  =  Wl  +  2W2  (16) 

Equation  (15)  then  becomes 

T\  +  Ti 
a  =  2(,    -l-^-  (17) 

The  equations  for  the  rail  pressures  RI  and  R2  hold  for  any 
values  of  TI  and  772  that  may  exisjt.  If  the  coefficient  of  adhesion 
be  represented  by  /i,  then 

T,  =  /A  (18) 

and 

T,  =  f,R2  (19) 

We  may  now  re-arrange  the  expressions  for  rail  pressures,  solv- 
ing them  for  TI  and  T2  from  equations  (18)  and  (19),  and  re- 
ducing by  the  substitution  of  values  of  W  and  a  from  equations 
(16)  and  (17).  Then 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     177 

fiW       Wb  +  2f,(Wih 


Wb  - 


Under  normal  conditions,  with  the  direction  of  motion  re- 
versible, the  greatest  pressure  that  can  be  applied  to  any  pair  of 
wheels  and  will  slide  none  of  them  may  be  determined  by  making 


T,  =  T2  =  f,R2  (22) 

Substituting  this  value  in  the  equation  for  R2,  and  simplifying 


V  _ 
4-  X  -  —  ^-  (23) 

Wb  +  2fl[Wi(h  +  ™)  +  2W2d] 

From  the  dimensions  of  standard  passenger  cars  without 
electrical  equipment,  and  assuming  a  coefficient  of  adhesion 

fiW 
fi  =  0.25,  it  is  found  that,  instead  of  having  a  value  of  —  j-  for 

fiW 

each  pair  of  wheels,  the  adhesion  is  only  0.834  —T—  •     Another 

way  of  looking  at  this  is  that  if  the  brake-shoe  pressures  are 
equal  on  all  wheels,  the  available  adhesion  for  obtaining  re- 
tardation is  only  83.4  per  cent,  of  the  total  weight  of  the  car. 
If  these  pressures  can  be  adjusted  to  allow  for  this  transfer  of 
weight  the  effectiveness  can  be  increased  over  16  per  cent. 

Although  it  is  not  practical  to  properly  alter  the  shoe  pressures 
between  the  two  trucks  without  changing  the  fixed  leverages 
of  the  brake  rigging,  it  is  possible  to  make  a  readjustment  of  the 
forces  acting  on  each  to  compensate  for  the  weight  transfer  from 
the  forward  to  the  rear  wheels  of  that  truck. 

In  common  practice,  the  brake  shoes  may  bear  on  the  wheels 
either  on  the  inside  or  the  outside  of  the  truck  frame.  Ordina- 
rily, they  are  placed  on  the  inside,  as  shown  in  Fig.  87.  When 
this  arrangement  is  used,  it  is  possible,  by  varying  the  angu- 
larity of  the  hanger  link,  to  introduce  a  force  which  will 
equalize  to  any  desired  degree  the  transfer  of  weight  from  the 
rear  to  the  forward  axle. 

In  Fig.  87  are  shown  the  forces  acting  on  the  truck  during  an 

application  of  the  brakes.    The  forces  P  and  P  are  those  supplied 
12 


178 


THE  ELECTRIC  RAILWAY 


from  the  brake  beam,  and  are  really  equally  divided  between  the 
two  wheels  at  opposite  ends  of  an  axle;  while  the  other  forces 
occur  separately,  but  generally  in  equal  amount,  at  the  individual 
contact  points.  As  mentioned  before,  it  is  simpler  to  treat  the 
pair  of  wheels  on  a  single  axle  as  one  unit.  Opposed  to  the 
brake-shoe  pressure  are  the  reactions  Qi  and  Q2  from  the  wheels, 
and  the  frictional  forces  FI  and  F2  result  from  these.  The  reac- 
tions on  the  brake  shoes  from  the  hanger  links  are  represented 
by  FI  and  F2.  The  middle  of  the  brake  shoes  is  usually  located 
a  small  distance  below  the  center  of  the  wheels;  the  angle  between 
the  direction  of  Qi  and  Q2  and  the  horizontal,  is  represented  by 
6  (by  similar  triangles).  The  mean  values  of  the  frictional 


FIG.  87. — Equalization  of  brake-shoe  pressure. 

By  properly  offsetting  the  brake  hangers,  the  weight  transfer  between  the  wheels  of  the 
truck  may  be  compensated,  allowing  a  greater  total  braking  force. 

forces  FI  and  F2  must  therefore  be  inclined  from  the  vertical  at 
the  same  angle.  In  the  particular  example  of  brake  rigging  shown, 
the  hanger  links  are  inclined  to  the  tangential  direction  of  the 
friction  by  the  angle  </>.  Resolving  the  forces  into  rectangular 
components,  referred  to  the  axes  of  the  hanger  links  for  each  pair 
of  wheels,  we  have 

Qi  cos  0  -  FI  sin  <j>  -  P  cos  (0  +  0)  =  0  (24) 

Q2  cos  </>  +  F2  sin  0  -  P  cos  (0  +  </>)=  0  (25) 

Now,  designating  the  coefficient  of  brake-shoe  friction  by  /2, 

Fi  =  f2Qi  (26) 

F2  =  /2Q2  (27) 


and 


Re-writing  equations  (24)  and  (25)  with  these  values  and  solving 
for      and  P 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     179 


tan  0  =  lT  (28) 

/2  ri  +  /*2 

p=  (Fi  +  ^)  cos  0  -  /2  (/?!  -  /?8)  sin  (fr 
2/2  cos 


Effect  of  Rotational  Inertia.  —  In  addition  to  destroying  the 
energy  of  translation  existing  in  the  moving  car,  the  brake-shoe 
friction  must  also  absorb  the  rotational  energy  of  the  wheels 
and  axles,  and  in  the  case  of  motor  cars  or  locomotives,  of  the 
motors.  This  inertia  is  entirely  independent  of  that  due  to 
translation;  and  in  destroying  it  the  coefficient  of  adhesion 
between  wheels  and  track  does  not  enter.  Practically,  a  greater 
braking  force  must  be  used  to  produce  a  given  retardation 
when  the  rotation  of  the  wheels  and  other  parts  is  taken  into 
consideration.1 

Letting  r  represent  the  radius  of  the  wheel,  the  retardation  a 

of  the  car  is  also  accompanied  by  a  retardation  -  in  the  motion 

of  the  wheel.  Calling  the  weight  of  one  wheel  and  one-half  of 
its  axle  w\,  and  the  radius  of  gyration  of  this  part  about  its  axis 
kij  the  retarding  force  necessary  to  be  applied  at  the  wheel  tread 
is 


for  a  truck  without  electrical  equipment.  For  a  motor  truck  this 
force  must  be  increased  by  the  amount 

55  /*•)•/*!)'„ 

g  \r  I    \nz/ 

where  w2  is  the  weight  and  kz  the  radius  of  gyration  of  the 
armature,  and  n\  and  n^  the  respective  numbers  of  teeth  on  the 
axle  gear  and  on  the  motor  pinion. 

The  total  retarding  forces  necessary  are,  therefore,  for  a  trailer 
truck, 

'  (30) 

a  (31) 


or,  for  a  truck  equipped  with  two  motors, 
1  Compare  Chapter  II,  "Rotational  Acceleration." 


180  THE  ELECTRIC  RAILWAY 

a       (32) 

(33) 


For  an  ordinary  pair  of  cast-iron  wheels  and  axle,  ~  =  0.64, 

and  (—  j     =  0.41;  using  these  values  in  equations  (30)  and  (31), 

and  replacing  TI  and  T2  by  their  values  found  in  equations  (20) 
and  (21),  we  have 


(W  +  3.28wi)  b  +  2/i  (Wih 

(34) 


/iTT  (Tf  +  3.28u)i)  6  -  2/i  (TTife 

4  (IF  +  ^,-3  6  (35) 

Substituting  these  values  in  equation  (28),  we  have 


2/,      WA  * 

*  =        - 


Equation  (29)  may  likewise  be  simplified  by  substituting 
the  value  of  Fi  —  F%  from  equation  (28)  : 

Fi  -  F2  =  /2  (Fi  +  F2)  tan  0  (37) 

whence 

/!  W  W  +  3.28^!   (1  -  /22  tan2  </>)  cos  0 

=  /24Tf  +  2/1TF1^          COS(^+</))  (38) 

From  this  last  equation  it  may  be  seen  that,  by  hanging  the 
brake  beams  between  the  wheels,  and  giving  the  proper  angle  of 
inclination  to  the  hanger  links,  the  pressure  may  be  increased 
on  the  forward  wheels  of  the  truck,  and  reduced  on  the  rear  wheels, 
with  corresponding  changes  in  the  frictional  force  produced. 
Reversing  the  direction  of  motion  transposes  the  distribution 
of  weight  between  the  two  axles  of  the  truck,  and  also  the 
actions  of  the  hanger  links,  so  that  the  greater  pressure  is  always 
applied  to  the  forward  wheels. 

The  worst  practical  difficulty  with  the  application  of  this 
method  of  compensation  of  the  brake-shoe  pressure  lies  in  the 
fact  that  the  angle  0  must  necessarily  vary  as  the  brake  shoes 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     181 

become  worn;  so  that  it  is  not  possible  to  make  the  compensa- 
tion the  same  under  all  conditions.  Any  desired  amount  may 
be  secured  up  to  the  point  where  skidding  occurs.1  The  practical 
values  of  6  +  0,  the  angle  the  hanger  should  make  with  the 
horizontal,  range  from  25°  to  37°,  depending  on  the  length  of 
wheel  base  and  diameter  of  wheels. 

Brake  Rigging. — In  any  form  of  brake  making  use  of  the 
friction  between  the  wheels  and  brake  shoes,  it  is  necessary  to 
have  a  system  of  levers  to  transmit  the  force  from  the  place 
where  it  is  developed  to  the  point  of  application.  The  general 
principles  are  the  same  for  all  brakes  of  this  class:  a  compara- 
tively small  force  is  applied  by  air  pressure  at  the  brake  cylinder, 
and  it  is  increased  considerably  through  the  lever  system.  This 
is  possible,  since  the  total  movement  of  the  shoes  to  give  the 
maximum  pressure  need  be  only  a  fraction  of  an  inch. 

The  subject  of  leverage  in  brake  rigging  is  primarily  one  of 
statics;  but  the  question  of  space  enters  in  making  allowance  for 
brake-shoe  clearance,  provision  for  wear  of  the  shoes,  wheels  and 
joints,  and  the  springing  of  members.  The  cylinders  of  stand- 
ard air-brake  apparatus  are  all  designed  to  give  a  normal  piston 
travel  of  about  8  in.  The  leverage  ratio  between  the  piston  and 
the  brake  shoes  varies  to  some  extent;  but  good  practice  calls 
for  values  between  the  limits  of  12  to  1  and  8  to  1.  By  this 
means  the  size  of  brake  cylinder  may  be  determined.  For 
example,  if  the  weight  of  a  certain  car  is  50,000  lb.,  and  100  per 
cent,  braking  force  is  to  be  applied  with  a  leverage  ratio  of  10 
to  1,  the  force  to  be  exerted  by  the  piston  is  5000  lb.  With  an 
emergency  air  pressure  of  70  lb.  per  sq.  in.,  this  will  require 
a  cylinder  with  an  inside  diameter  of  9.55  sq.  in.  Since  the 
standard  diameters  of  brake  cylinders  increase  by  increments  of 
2  in.;  a  10-in.  cylinder  will  be  required. 

Having  determined  the  proper  size  of  cylinder,  the  brake  rigging 
for  the  trucks  and  car  body  may  be  calculated.  There  are  three 
different  arrangements  for  applying  the  brake  shoes:  the  brakes 
may  be  hung  inside  the  wheels;  they  may  be  hung  outside;  or 
both  may  be  used.  The  latter  type  is  usually  known  as  the 
*  'clasp  brake."  Of  the  first  two,  the  inside  hung  brakes  are  pref- 
erable, for  reasons  already  discussed.  In  some  cases  it  may  be 
advantageous  to  hang  the  shoes  outside  the  wheels  for  structural 

1  For  a  further  discussion  of  this  topic,  see  Transactions  A.  I.  E.  E., 
Vol.  XX,  p.  264. 


182 


THE  ELECTRIC  RAILWAY 


reasons.  With  either  inside-hung  or  outside-hung  brakes,  there 
is  an  unbalanced  pressure  which  must  be  opposed  by  a  reaction 
from  the  wheel.  This  reaction  is  furnished  by  the  brasses  in  the 
journal  boxes.  In  the  case  of  heavy  high-speed  trains,  which 
have  to  be  retarded  rapidly,  the  braking  pressures  become  ex- 
cessive. This  may  cause  the  brasses  to  wear  more  on  the  side 
away  from  the  brake  shoes,  and  even  force  them  out  of  position. 
To  remedy  this  trouble,  a  number  of  railroads  operating  high- 
speed trains  have  adopted  the  clasp  brake,  for  this  type  places 
equal  brake-shoe  pressures  on  opposite  sides  of  the  wheel,  thus 
removing  the  reactions  from  the  bearings. 

Truck  Brake  Rigging. — In  applying  the  braking  force  to  the 
truck,  it  must  be  distributed  equally  to  all  of  the  brake  shoes, 
or  there  will  be  danger  of  sliding  the  wheels.  If  it  is  desired  to 
increase  the  braking  force  on  the  front  wheels,  this  should  be  done 


Live  Lever 


Dead  Lever 


\ 


FIG.  88. — Truck  brake  rigging  for  electric  car. 


The  force  delivered  by  the  pull  rod  is  transmitted  through  the  live  lever  and  the  bottom 
rod  (sometimes  known  as  the  adjusting  rod)  to  the  dead  lever,  thus  applying  the  brakes. 

by  giving  the  hangers  the  proper  angle.  The  force  can  be  applied 
to  the  four  shoes  separately,  by  having  independent  lever  systems 
for  each  side,  or  together,  through  brake  beams.  These  latter 
are  used  to  a  large  extent  on  freight  cars;  but  on  electric  motor 
cars  there  is  seldom  sufficient  room  for  them  with  inside-hung 
brakes,  so  that  separate  levers  are  used,  being  connected  together 
with  a  bar  to  which  the  main  pull  rod  is  fastened. 

When  brakes  are  applied  to  double-truck  electric  cars  which 
must  travel  around  sharp  curves,  the  plain  bar  for  connecting 
the  truck  brake  levers  together  is  sometimes  not  sufficient  to 
provide  for  the  excessive  swiveling.  In  such  cases  the  bar  is 
made  in  the  form  of  a  circular  arc,  technically  known  as  a  "radius 
bar/'  and  the  brake  pull  rod  is  connected  to  it  through  a  roller 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     183 

working  in  a  clevis.  The  truck  can  then  swivel  any  needed 
amount  without  interfering  with  the  action  of  the  brakes. 

The  usual  arrangement  of  the  brake  rigging  without  brake 
beams  is  shown  in  Fig.  88.  The  use  of  the  radius  bar  and  the 
relations  of  the  levers  may  be  clearly  seen.  It  may  be  noted  that, 
by  fastening  one  end  of  the  "dead  lever"  to  the  truck  frame,  the 
reaction  of  the  brake  shoe  on  the  live  lever  is  transmitted  to  the 
other  shoe,  so  that  the  force  applied  gives  double  the  braking 
effort  produced  on  a  single  shoe. 

Foundation  Brake  Rigging. — In  Fig.  89  is  shown  a  common 
arrangement  of  the  essential  parts  of  the  brake  rigging  attached  to 
the  car  body.  The  air  pressure  acting  on  the  piston  operates 

fulcrum 
ffand  Brake  Rod 


FIG.  89. — Foundation  brake  rigging. 

A  form  of  brake  rigging  in  very  common  use.      Note  the  method  of  connecting  the  hand 
brakes  so  as  not  to  interfere  with  the  action  of  the  air-brake. 

the  push  rod  and  the  push-rod  lever,  and,  with  the  aid  of  the 
cylinder  rod,  applies  the  requisite  forces  to  the  brake  riggings 
of  the  two  trucks.  It  is  always  desirable  to  provide  hand  brakes 
for  emergencies,  in  case  of  failure  of  the  air  supply,  or  where  it  is 
necessary  to  hold  the  car  after  the  air  pressure  has  been  cut  off. 
This  connection  may  be  made  to  the  push  rod,  as  shown,  the 
leverage  on  the  hand-brake  system  being  such  as  to  produce  the 
same  total  braking  force  as  when  air  is  used.  Other  arrangements 
may  be  made. 

The  calculation  of  the  proper  lengths  of  the  various  levers  is 
simple  after  the  brake-shoe  pressures  have  been  decided  on.  It 
will  be  different  for  each  individual  lever  arrangement.  To 
show  the  method  of  calculation,  the  determination  for  a  typical 
car  will  be  taken  up. 


184  THE  ELECTRIC  RAILWAY 

Example. — A  certain  car,  whose  principal  weights  are  given 
below,  is  to  be  fitted  with  brakes.  The  electrical  equipment 
consists  of  two  motors,  both  mounted  on  one  truck,  the  other 
truck  being  a  trailer.  Connections  for  both  air  and  hand  brakes 
are  to  be  provided,  it  being  assumed  that  the  platform  leverage 
system  of  the  hand  brake  is  such  that  the  average  motorman  can 
produce  a  force  of  1200  Ib.  in  the  pull  rod  connected  to  the  main 
lever  system.  It  is  desired  to  determine  the  lengths  of  all 
levers,  and  the  forces  in  all  parts  of  the  brake  rigging. 

Weight  of  car  body  and  apparatus  supported  thereon  40,000  Ib. 

Weight  of  motor  truck 10,000  Ib. 

Weight  of  trailer  truck 6,000  Ib. 

Weight  of  each  motor 4,000  Ib. 

The  motor  truck  is  to  have  inside-hung  brake  shoes  without 
brake  beams.  Both  the  live  and  the  dead  levers  have  lengths  of 
27  in.,  the  brake  shoes  being  hung  7  in.  from  the  lower  end. 

The  trailer  truck  is  to  have  outside  hung  brake  shoes  with 
brake  beams,  the  live  and  dead  levers  both  being  23  in.  long  with 
shoes  hung  7  in.  from  the  lower  end. 

The  braking  force  on  the  motor  truck  is  to  be  100  per  cent, 
of  the  weight  carried,  and  on  the  trailer  truck  90  per  cent,  of  the 
weight. 

The  weight  on  the  wheels  of  the  motor  truck  is 

20,000  +  10,000  +  2  X  4000  =  38,000  Ib. 

or  9500  Ib.  per  wheel.     The  brake-shoe  pressure  to  be  applied  is, 
therefore,  at  100  per  cent.,  9500  Ib. 

The  weight  carried  by  the  wheels  of  the  trailer  truck  is 

20,000  +  6000  =  26,000 

This  corresponds  to  6500  Ib.  per  wheel.     At  90  per  cent,  braking 
force  the  pressure  per  shoe  is  5850  Ib.     Since  a  brake  beam  is  to 
be  used,  the  force  for  the  two  sides  must  be  supplied  at  one  point, 
making  a  total  of  11,700  Ib.  on  the  brake  beam. 
The  total  braking  power  needed  is 

9500  X  4  +  H,700  X  2  =  61,400  Ib. 

If  a  12-in.  diam.  cylinder  is  used,  a  pressure  of  60  Ib.  on  the 
piston  will  give  a  total  of  6780  Ib.  This  will  make  the  total 
leverage  ratio 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     185 
61,400 


6780 


=  9.05 


which  is  a  conservative  value  for  a  car  of  this  type. 

On  the  motor  truck,  the  dead-lever  fulcrum  being    at    the 
upper  end,  the  force  in  the  adjusting  rod  is 

20  X  9500 

0-       -  =  7040  Ib. 

Z  ( 

With  the  live-lever  fulcrum  at  the  bottom,  the  pull  at  the  top  is 
9500  X  7 


27 


2460  Ib. 


The  proof  of  this  last  calculation  is  that  the  sum  of  the  force 
at  the  top  and  bottom  of  the  live  lever  must  be  equal  to  the  press 
sure  on  the  shoe. 

2460  +  7040  =  9500  Ib. 

Since  there  is  a  duplicate  set  of  shoes  and  levers  on  either  side 
of  the  truck,  the  total  stress  in  the  pull  rod  is  twice  that  found, 
or, 

2  X  2460  =  4920  Ib. 

On  the  trailer  truck,  with  the  dead-lever  fulcrum  at  the  upper 
end,  the  force  in  the  adjusting  rod  is 

ll.TOOXJ*  X1 

In  the  live  lever,  with  the  fulcrum  at  the  adjusting  rod,  the  force 
at  the  top  is 


As  above,  this  is  proved  as  follows: 

16,800  =  5100  +  11,700 

At  the  brake  cylinder,  the  force  on  the  push  rod  is  6780;  hence 
the  force  on  the  cylinder  rod  is 

6180  +  5100  =  11,880  Ib. 
The  length  a  is  therefore 

6780  ^  SO 

=  17.1  in.  (in  practice  17>£  in.) 


186  THE  ELECTRIC  RAILWAY 

and  the  length  6  is 

30  -  17%  =  12%  in. 

For  the  cylinder  lever,  the  length  d  is 
4920  X  30 


11,880 
and  c  is  therefore 


12.41  in.   (in  practice 


in.) 


30  -  12%  =  17%  in. 
With  a  force  of  1200  Ib.  acting  on  the  hand-brake  rod,  which 


To  Hand  drake 

"KoeTiS.      7,  R*cd 

;    \ 

J    \'°" 

&".'         \  67801k 


2>3901b. 


k- 

Fixtd-rf 

»**  %*  «u 

/?  \r 

\      J    K800lb\ 

l\l 

I      \l7000ik 


24601k          Fixed 
Ib.20"   20\9SOOIk 


2460  Ib.          Fixed 
9500 Ib   ho"    20\      9500 Ib. 


7* 

70401k 


FIG.  90. — Distribution  of  forces  in  foundation  brake  rigging. 

must  be  increased  to  6780  Ib.,  the  force  required  at  the  end  of 
the  multiplying  lever  is 


The  length  from  the  fulcrum  to  the  point  of  connection  is 
therefore 

1200  X  36       10_.  ,         ,.     „     1oqx  .    , 
339Q  —  =  12.74  (practically  12%  in.) 

In  order  that  the  levers  may  be  parallel  when  the  slack  ad- 
juster is  half  way  out,  and  the  piston  is  at  the  end  of  its  normal 
stroke,  the  length  of  the  cylinder  rod  must  be 

20  +  5  +  5  =  30  in. 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     187 

A  movement  of  J£  in.  at  each  shoe  on  the  motor  truck  will 
give  a  movement  at  the  push  rod  of 

27        1  2  "37  ^0 

(M  X  2)  X  y  X  -™  X  jy^  =  L393  in' 

A  similar  movement  of  Y±  in.  at  each  shoe  on  the  trailer  truck 
will  give  a  movement  at  the  push  rod  of 

1  fi        12  88 
(MX  2)  X  y  X  ~^  =  0.86  in. 

The  total  movement  of  the  push  rod  is 

1.393  +  0.86  =  2.25  in. 

and,  adding  %  in.  for  lost  motion,  the  travel  necessary  for  the 
push  rod  to  apply  the  maximum  braking  force  is  approximately 


Automatic  Slack  Adjuster.  —  The  amount  of  air  needed  for 
producing  a  certain  cylinder  pressure  depends  on  the  piston  travel, 
so  that  it  is  desirable  to  keep  this  as  short  as  possible.  With  the 
automatic  brake,  where  the  cylinder  is  supplied  from  an  auxiliary 
reservoir  of  small  capacity,  excessive  piston  travel  will  result  in 
reduced  cylinder  pressure,  and  consequently  smaller  braking 
effort.  The  best  operation  is  obtained  when  the  piston  travel  is 
just  sufficient  to  allow  proper  clearance  of  the  shoes  when  the 
brakes  are  released.  On  standard  equipments  this  calls  for  a 
running  travel  of  about  8  in.  Any  greater  movement  simply 
calls  for  more  air  or  for  less  efficient  braking. 

Various  forms  of  automatic  slack  adjusters  are  on  the  market. 
The  best  known  of  these  is  shown  in  Fig.  89.  A  small  connec- 
tion is  made  through  the  brake-cylinder  wall  at  a  point  deter- 
mined by  the  maximum  desirable  piston  travel.  When  this  is 
exceeded  air  is  admitted  to  the  tap,  and  serves  to  operate  a 
ratchet,  changing  the  position  of  the  lever,  as  indicated  in  the 
diagram.  Each  time  the  brakes  are  applied  when  the  travel 
is  greater  than  the  desired  amount,  the  ratchet  will  move  one 
notch,  until  the  excess  has  all  been  taken  up,  after  which  no 
further  action  of  the  slack  adjuster  will  take  place  until  the 
slack  has  again  passed  the  limiting  value,  and  the  piston  travel 
has  become  too  great. 

Methods  of  Supplying  Braking  Force.  Hand  Brakes.  —  The 
brake  rigging  described  will  work  equally  well  with  any  available 


188  THE  ELECTRIC  RAILWAY 

force  that  can  be  applied  in  the  proper  amount,  and  with  proper 
control.  Two  methods  of  operation  have  been  suggested — 
manual  and  air  pressure  being  used.  With  hand  brakes,  the 
force  is  applied  to  a  brake  staff  by  means  of  a  cranked  handle  or 
hand-wheel  turned  by  the  motorman.  The  staff  carries  at  its 
lower  end  a  chain  which  is  attached  to  the  pull  rod  connecting 
to  the  foundation  brake  rigging.  By  rotating  the  brake  staff 
the  chain  is  wrapped  about  it,  thus  applying  the  braking  force 
to  the  rigging.  If  the  car  is  heavy,  and  the  necessary  retarding 
force  is  large,  it  is  sometimes  impossible  to  get  sufficient  leverage 
with  this  arrangement.  To  increase  the  pull,  the  bottom  of 
the  brake  staff  may  carry  a  gear,  the  chain  connection  to  the 
pull  rod  being  made  through  the  meshing  gear.  The  force  may 
thus  be  increased  to  any  desired  value.  A  limitation  may  be 
seen  in  various  forms  of  high-ratio  hand  brakes,  in  that,  if 
designed  to  give  the  maximum  braking  force  when  applied 
by  the  average  motorman,  there  is  a  great  risk  of  skidding  the 
wheels  when  operated  by  a  stronger  man.  This  is  something 
which  cannot  be  taken  care  of  in  the  design,  and  may  result  in 
the  use  of  hand  brakes  of  less  power  merely  to  obviate  this 
danger. 

In  the  operation  of  hand  brakes,  it  is  necessary,  as  in  any 
case,  to  have  a  certain  amount  of  " slack"  in  the  rigging.  This 
is  needed  to  keep  the  shoes  away  from  the  wheels  when  the  brakes 
are  released.  The  ordinary  motorman,  in  making  a  stop,  de- 
sires to  apply  the  brakes  as  soon  as  possible  after  the  signal  has 
been  given,  or  the  proper  place  for  their  operation  has  been 
reached.  In  order  to  prevent  loss  of  time  in  making  the  appli- 
cation, it  is  often  the  custom  among  motormen  to  run  the  cars 
with  the  slack  all  taken  out  of  the  brake  rigging,  the  shoes  being 
as  near  the  wheels  as  possible  without  applying  the  brakes. 
This  is  done  by  winding  the  spare  chain  on  the  brake  staff, 
and  holding  the  handle  in  that  position  continually.  When 
operating  in  this  manner,  it  is  almost  impossible  to  keep  from 
having  some  friction  of  the  shoes  on  the  wheels.  This,  in  effect, 
is  the  same  as  increasing  the  train  resistance;  and  it  requires 
additional  power  from  the  electric  circuit.  In  certain  cases 
where  air  brakes  have  been  added  to  cars  already  in  use  with 
hand  brakes  only,  it  has  been  found  that  there  has  been  a  marked 
decrease  in  the  power  consumption,  sometimes  amounting  to 
as  much  as  15  to  20  per  cent. 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     189 

Air  Brakes. — Of  all  the  forms  of  power  brakes  which  have  been 
developed,  the  one  which  has  met  with  the  greatest  success  and 
has  been  most  widely  adopted,  is  that  in  which  the  braking  force 
is  produced  by  means  of  compressed  air.  Generally  speaking, 
compressed  air  is  admitted  to  the  brake  cylinder,  and  the  piston 
operates  a  push  rod  connected  to  the  rigging.  The  principal 
difference  in  various  types  of  brakes  is  in  the  methods  by  which 
the  admission  and  release  of  air  to  the  cylinder  is  controlled.  The 
two  methods  in  general  use  are  the  "  straight "  and  the  "  auto- 
matic" systems.  In  the  former,  air  is  applied  directly  to  the  brake 
cylinder  from  a  main  reservoir;  in  the  second,  it  is  supplied  to  the 
cylinder  from  an  auxiliary  reservoir,  the  main  air  pressure  being 
used  to  control  the  admission  of  air  to  and  from  the  latter,  and 
the  release  of  the  air  from  the  brake  cylinder  to  the  outside 
atmosphere. 

Methods  of  Compressing  the  Air. — Another  way  in  which 
systems  of  air  brakes  differ  is  due  to  the  methods  in  use  for  sup- 
plying the  compressed  air.  The  simplest  arrangement  is  to 
provide  large  stationary  compressors  at  suitable  points  along  the 
railroad.  These  plants  continuously  charge  stationary  reser- 
voirs of  large  capacity.  Each  car  is  provided  with  a  storage  tank, 
which  may  be  charged  from  the  stationary  reservoirs  as  needed, 
the  operation  taking  but  a  few  minutes  as  the  car  reaches  the 
charging  station.  In  order  to  reduce  the  size  of  the  car  reservoir, 
the  air  is  stored  at  high  pressure  (about  300  Ib.  per  sq.  in.). 
For  use  in  the  cylinders,  this  is  reduced  to  about  45  Ib.  per 
sq.  in.,  which  causes  a  certain  loss  in  efficiency. 

The  more  common  method  of  supplying  the  compressed  air 
is  by  means  of  individual  compressors,  located  on  the  cars  or 
locomotives.  For  steam  service,  the  compressors  are  driven 
directly  by  steam  from  the  boiler,  there  being  one  or  more  installed 
on  each  locomotive,  depending  on  the  capacity  required.  For 
service  on  electric  roads,  the  steam  pump  is  replaced  by  one  driven 
either  from  gearing  connected  to  the  axle,  or  by  an  individual  elec- 
tric motor.  The  axle-driven  compressors  were  favored  in  the 
early  period  of  air-brake  operation  on  electric  roads;  but,  owing 
to  a  number  of  difficulties  in  construction,  and  high  maintenance 
costs,  they  have  been  almost  entirely  susperseded  by  motor- 
driven  compressors. 

The  motor-driven  compressor  may  be  either  a  simple  or  a  two- 
stage  air  pump  of  the  reciprocating  type,  operated  direct  or 


190  THE  ELECTRIC  RAILWAY 

through  gearing  by  a  small  series  motor,  in  the  case  of  direct- 
current  or  single-phase  roads;  or  by  an  induction  motor  on  three- 
phase  lines.  In  systems  using  individual  compressors,  where 
the  reservoir  can  be  charged  as  often  as  required,  the  pressure 
range  is  between  50  and  90  lb.;  the  limits  between  the  maximum 
and  the  minimum  values  usually  being  about  20  Ib.  (e.g.,  between 
70  and  90  Ib.  is  the  range  on  many  systems). 

To  keep  the  pressure  in  the  reservoir  within  the  proper  limits, 
intermittent  operation  of  the  air  compressor  is  necessary.  The 
action  is  controlled  automatically  by  some  form  of  governor 
which  connects  the  motor  to  the  line  when  the  pressure  has  fallen 
to  the  minimum  limit,  and  opens  the  circuit  when  it  has  been 
increased  to  the  maximum.  Various  types  of  governor  are  in 
use,  but  the  basic  principle,  as  stated  above,  is  the  same  in  all. 

Straight  Air  Brakes. — The  simplest  method  of  supplying  the 
air  to  the  brake  cylinder  is  obviously  that  in  which  it  is  admitted 
directly  from  the  main  reservoir.  The  control  for  this  type  of 
brake  consists  essentially  of  a  valve  operated  by  the  motorman, 
which  can  connect  the  cylinder  to  the  main  reservoir,  can  dis- 
connect it  and  retain  the  air,  or  can  release  the  air  completely 
from  the  cylinder  by  connecting  it  with  the  atmosphere. 

For  single-car  operation,  the  straight  air  brake  is  ideal,  for  the 
motorman  can  graduate  the  amount  of  air  admitted  to  the  cylinder 
and  thereby  adjust  the  braking  force  to  obtain  uniform  retardation 
in  spite  of  the  variable  coefficient  of  friction.  As  the  length  of  the 
train  is  increased,  difficulty  is  experienced  in  getting  uniform 
application  of  the  brakes.  All  the  air  which  enters  the  cylinders 
must  flow  from  the  main  reservoir  on  the  forward  car  or  locomo- 
tive, through  the  controlling  valve,  and  then  through  a  train 
pipe  to  the  brake  cylinders  on  the  individual  cars.  It  is  evident 
that  the  pressure  will  build  up  at  the  front  end  of  the  train  first ; 
and  that  a  considerable  time  will  elapse  before  the  brakes  are 
applied  with  full  force  on  the  last  car  of  the  train.  This  variation 
in  force  at  the  instant  when  the  brakes  are  applied  may  cause 
trains  to  break  in  two,  resulting  in  serious  accidents;  and  at  best 
imposes  severe  strains  on  the  drawbars. 

Automatic  Air  Brakes. — To  obviate  the  troubles  incident  to  the 
use  of  straight  air  brakes  on  trains  of  considerable  length,  the 
automatic  air  brake  was  developed.  In  this  system  the  train 
pipe  does  not  feed  directly  into  the  brake  cylinders,  but  is  used 
to  charge  a  main  reservoir  on  the  locomotive  and  a  set  of  auxiliary 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     191 

reservoirs,  one  of  which  is  located  on  each  car.  In  the  normal 
running  position,  all  of  the  latter  are  fully  charged  to  the  train 
pipe  pressure,  and  the  brake  cylinders  are  open  to  the  outside 
atmosphere. 

These  relations  are  controlled  by  a  device  known  as  the 
"  triple  valve,"  shown  in  Fig.  91,  which  automatically  makes 
the  proper  connections  between  the  train  pipe,  the  auxiliary 
reservoir,  the  brake  cylinder,  and  the  outside  atmosphere.  It 
is  evident  that  a  triple  valve  is  a  necessary  part  of  the  equip- 
ment of  each  car  in  the  train. 


To  Auxiliary 

Reservoir 

A 


Jo  drake 
Cylinder 


Jo    rain 
FIG.  91. — Plain  triple  valve. 

As  shown,  the  brake  cylinder  is  exhausting  to  the  outside  atmosphere,  and  the  auxiliary 
reservoir  is  being  charged  from  the  train  pipe.  This  is  the  release  or  running  position.  A 
reduction  in  train  pipe  pressure  causes  the  slide  valve  to  move  to  the  left,  closing  the  connec- 
tion between  the  train  pipe  and  the  auxiliary  reservoir,  and  connecting  the  latter  to  the  brake 
cylinder,  the  exhaust  being  closed  at  the  same  time. 

To  apply  the  brakes,  the  train  pipe  pressure  is  suddenly  re- 
duced, which  causes  a  movement  of  the  triple  valve,  disconnect- 
ing the  auxiliary  reservoir  from  the  train  pipe,  and  connecting 
it  with  the  brake  cylinder,  meanwhile  closing  the  exhaust  con- 
nection. This  causes  the  air  to  flow  from  the  auxiliary  reservoir 
to  the  brake  cylinder,  applying  the  brakes.  Various  improve- 
ments have  been  made  from  time  to  time  to  increase  the  rapidity 
with  which  the  train-pipe  pressure  is  lowered,  and  to  make  the 
movement  of  the  triple  valve  with  a  minimum  reduction  in 
pressure.  In  the  well-known  "  quick-action "  brake,  which  is 
in  use  on  a  large  proportion  of  the  steam  roads,  the  train  pipe 
is  vented  directly  into  the  brake  cylinder  by  the  movement  of 


192  THE  ELECTRIC  RAILWAY 

the  triple  valve.  In  this  way  the  reduction  in  train-pipe  pressure 
can  be  made  in  a  very  short  time,  requiring  only  a  few  seconds 
for  the  longest  freight  trains  in  operation.  In  making  an 
ordinary  or  " service"  application,  the  full  pressure  available 
from  the  auxiliary  reservoir  is  not  needed.  When  the  desired 
amount  of  air  has  been  admitted  to  each  brake  cylinder,  its 
triple  valve  is  closed.  To  produce  this  effect  the  train-pipe 
pressure  need  only  be  lessened  a  small  amount;  in  the  standard 
types  of  brake  this  reduction  must  not  exceed  about  15  Ib. 
With  a  greater  drop  in  the  train  pipe  the  " emergency"  applica- 
tion occurs,  in  which  the  train  pipe  is  fully  vented  to  the  atmos- 
phere or  to  the  cylinders,  and  the  full  pressure  from  the  auxiliary 
reservoir  is  applied  to  the  brakes. 

To  release  the  brake,  the  engineer's  valve  is  moved  to  such  a 
position  as  to  admit  air  from  the  main  reservoir  to  the  train  pipe. 
This  increase  in  train-pipe  pressure  changes  the  position  of 
the  triple  valve  so  as  to  close  the  connection  between  the  auxiliary 
reservoir  and  the  brake  cylinder,  connecting  the  former  to  the 
train  pipe.  This  recharges  the  auxiliary  reservoir.  At  the  same 
time  the  brake  cylinder  is  connected  to  the  atmosphere,  which 
releases  all  the  air  and  removes  the  pressure  from  the  piston  and 
from  the  brakes. 

A  modification  of  the  quick-action  brake,  known  as  the 
" high-speed"  brake,  has  been  developed  for  use  on  fast  passenger 
trains.  In  the  design  of  this  brake,  account  is  taken  of  the 
fact  that  the  coefficient  of  friction  is  less  at  high  speeds.  The 
train-pipe  pressure  in  this  type  is  higher  than  in  the  quick-action 
brake,  being  in  the  neighborhood  of  110  Ib.  When  the 
emergency  application  is  made,  the  full  pressure  is  applied  from 
the  auxiliary  reservoirs  to  the  cylinders,  producing  a  braking  force 
which,  although  not  sufficient  to  cause  sliding  of  the  wheels  at 
the  high  speed,  would  almost  certainly  do  it  before  stopping 
the  train.  To  prevent  such  a  result,  the  pressure  is  lowered 
gradually,  by  means  of  an  automatic  reducing  valve  on  the  car, 
to  the  emergency  standard  of  60  Ib. 

Electropneumatic  Brake. — Although  the  quick-action  and 
the  high-speed  brakes  have  been  very  satisfactory  in  general  serv- 
ice, conditions  arise  in  connection  with  the  operation  of  heavy, 
fast  trains,  where  the  control  they  exercise  is  not  sufficient.  Even 
with  the  quick-actiori  brake,  there  is  a  certain  time  lag  between 
the  movement  of  the  engineer's  valve  and  the  application  of  the 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     193 

brakes  on  the  rear  car  of  the  train.  Where  the  trains  are  short, 
or  where  the  speeds  are  low,  this  will  cause  no  difficulty  in  opera- 
tion. With  long,  high-speed  trains  there  is  considerable  surging 
of  the  cars,  and  strain  on  the  draft  rigging.  Further  than  this,  the 
time  required  for  the  full  application  of  the  brakes  makes  the  total 
distance  from  the  braking  signal  to  a  stop  materially  longer  than 
if  the  brakes  were  all  set  simultaneously.  A  certain  time  element 
is  unavoidable,  for  the  air  cannot  flow  from  the  auxiliary  reservoir 
to  the  brake  cylinder  instantaneously;  but  beyond  this,  it  is  de- 
sirable to  eliminate  the  lag.  This  is  accomplished  by  the  use  of 
the  electropneumatic  brake.  In  this  type,  the  ordinary  features 
of  the  automatic  brake  are  retained,  but  the  application  of  the 
pressure  is  governed  by  an  electric  circuit,  in  a  manner  somewhat 
similar  to  that  of  the  electropneumatic  control  of  the  motor 
circuits  in  multiple-unit  operation.  A  special  form  of  triple 
valve  is  used,  in  which  the  admission  of  air  to  the  brake  cylinders 
is  governed  by  electromagnetic  valves.  By  proper  combinations 
of  electric  circuits  the  brake  cylinder  pressure  may  be  built  up 
to  the  maximum,  may  be  held  in  the  cylinders,  or  may  be  wholly 
or  partially  exhausted.  This  latter  feature  is  of  great  impor- 
tance, since  with  the  ordinary  automatic  brake  there  is  little  oppor- 
tunity to  provide  a  graduated  release. 

A  comparison  of  the  action  of  the  two  types  of  brake  is  shown 
in  Fig.  92. 1  In  the  pneumatically  controlled  brake,  the  stop  is 
made  in  40  seconds  from  the  time  the  brake  application  was  be- 
gun, bringing  the  train  to  rest  in  a  distance  of  1290  ft.  In  this 
operation  a  graduated  action  was  obtained  by  increasing  the 
train-pipe  pressure  to  release  the  brakes  and  then  partially  re- 
applying  them.  In  comparison,  with  this,  the  electrically  con- 
trolled brakes  brought  the  train  to  rest  after  20  seconds,  or  one- 
half  the  time  required  for  the  pneumatic,  the  distance  taken  being 
700  ft.  In  the  operation  of  the  electrically  controlled  brake,  a 
much  more  effective  graduation  of  the  release  was  obtained,  there 
being  two  partial  reductions  of  pressure.  The  result  can  be  seen 
in  the  more  uniform  slope  of  the  speed-time  curve.  Due  to  this 
feature,  the  maximum  braking  effort  can  be  increased  to  a  value 
which  would  be  dangerous  for  the  ordinary  automatic  brake.  It 
should  be  noted  that  the  final  pressure  at  the  end  of  the  stop  is 

1  Figs.  92  and  93  are  from  an  article  by  W.  V.  TURNER,  Electric  Journal, 
Vol.  VIII,  p.  905,  Oct.,  1911. 

13 


194 


THE  ELECTRIC  RAILWAY 


1500 


36 


4Z 


24         30 
Time,  Seconds. 
FIG.  92. — Service  stops  with  automatic  and  electropneumatic  brakes. 

Note  that  the  pressure  builds  up  much  more  rapidly  in  the  electropneumatic  application; 
also  that  the  release  is  gradual,  while  in  the  automatic  application  the  brakes  were  released 
and  then  re-applied  to  reduce  the  pressure. 


bis  fa  nee,  Automatic 
store  Elec.  Pneu. 


18          24        30 
Time,  Seconds 
FIG.  93. — Emergency  stops  with  automatic  and  electropneumatic  brakes. 

In  addition  to  using  a  higher  braking  force,  it  is  possible  to  build  up  the  pressure  more 
rapidly  with  the  electropneumatic  brake,  resulting  in  a  considerable  reduction  both  in  time 
and  distance  required  for  stopping  a  train. 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     195 

less  with  the  electropneumatic  control  than  with  the  common 
type. 

In  emergency  stops  the  advantage  of  simultaneous  action  of 
the  brakes  on  all  the  cars  is  much  greater  than  for  service  applica- 
tions. A  typical  comparison  of  emergency  stops  is  shown  in 
Fig.  93,  which  has  been  plotted  to  the  same  scales  as  Fig.  92. 
It  may  be  seen  that  the  total  distance  for  the  stop  is  300  ft.  less 
for  the  electric  brake,  or  only  slightly  over  half  that  for  the 
pneumatic.  The  time  for  stopping  the  train  is  likewise  decreased 
from  22  seconds  to  11  seconds.  The  use  of  the  electric  con- 
trol makes  possible  a  considerable  reduction  in  the  distance 
interval  which  must  be  allowed  between  trains  for  safety,  so  that 
track  capacity  may  be  materially  increased. 

Combined  Straight  and  Automatic  Brake. — Many  electric 
roads  operate  their  cars  singly  for  the  greater  portion  of  the  time, 
but  occasionally  run  trains  of  two  or  three  cars.  For  single-car 
service  the  straight  air  brake  gives  all  the  desired  features  and 
is  easier  to  manipulate  than  the  automatic.  But  when  cars  are 
coupled  together,  the  use  of  the  straight  air  brake,  even  on  com- 
paratively short  trains,  leads  to  the  difficulties  due  to  slow  trans- 
mission of  the  braking  force  to  the  rear  of  the  train.  For  such 
cases  it  is  possible  to  have  a  combined  equipment,  which  for 
normal  operation  acts  as  a  straight  air  brake,  but  may  be  quickly 
converted  into  an  automatic  brake  by  the  change  in  a  few  valve 
connections.  A  number  of  variations  in  the  arrangement  of  the 
valves  is  possible,  and  several  types  of  combination  brake  are  in 
use. 

Vacuum  Brake. — Although  the  air  brake  is  in  almost  universal 
use  in  this  country,  it  has  a  competitor  in  Europe  in  the  vacuum 
brake.  In  this  type  the  principle  of  operation  is  almost  identical 
with  that  of  the  air  brake,  but  the  compressed  air  is  replaced  by 
a  partial  vacuum,  produced  by  a  pump  somewhat  similar  to  the 
ordinary  air-compressor.  Since  the  pressure  in  the  brake  cylinder 
depends  on  the  unbalanced  action  of  the  external  air  on  the  piston, 
it  follows  that  the  maximum  force  which  can  be  obtained  is  15 
Ib.  per  sq.  in.  In  order  to  get  the  same  brake-shoe  pressures 
as  are  ordinarily  in  use,  the  size  of  cylinders  must  be  consider- 
ably increased.  In  general,  the  operation  of  .this  brake  is  infe- 
rior to  the  modern  air  brakes  described  above. 

Electric  and  Magnetic  Brakes. — A  number  of  attempts  to 
utilize  electric  energy  for  the  braking  of  trains  have  been  made 


196  THE  ELECTRIC  RAILWAY 

from  time  to  time.  The  simplest  of  these  consists  of  a  disc, 
fastened  to  the  axle,  and  a  circular  electromagnet  attached  to  the 
truck.  The  magnet,  when  energized  with  current  from  the  trolley 
wire,  may  be  made  to  bear  against  the  disc.  This  type  of  brake 
was  developed  a  number  of  years  ago;  but  it  never  was  very 
successful,  and  is  now  obsolete.  A  much  simpler  arrangement  is 
to  reverse  the  car  motors  and  connect  them  to  the  line.  This 
produces  a  counter  torque,  giving  a  powerful  retarding  effort. 
Both  of  these  methods  of  braking  require  the  use  of  electric 
energy  from  the  line,  and  the  second  increases  the  duty  of  the 
motors. 

It  has  already  been  shown  that  a  moving  car  possesses  a 
considerable  amount  of  stored  energy,  due  to  its  velocity.  It 
would  seem  desirable  to  utilize  this  in  stopping  the  car  in  some 
other  way  than  to  waste  it  in  heating  the  brake  shoes  and  wheels. 
If  the  motors  can  be  made  to  reverse  their  usual  functions  and  act 
as  generators,  they  will  convert  the  kinetic  energy  of  the  moving 
train  into  electricity,  which  may  be  returned  to  the  line  or  used 
for  some  other  purpose.  The  greatest  obstacle  in  the  way  of 
returning  energy  with  ordinary  equipments  is  that  the  series  motor 
does  not  readily  lend  itself  to  this  use.  If  allowed  to  operate 
without  change  of  connections,  it  cannot  be  made  to  exert  a 
counter-torque,  since  the  speed  increases  indefinitely  as  the 
load  is  reduced.  On  the  other  hand,  if  the  field  is  reversed,  the 
counter  e.m.f.  will  be  in  the  same  direction  as  the  line  e.m.f.,  so 
that  the  motor  will  give  a  counter-torque,  but  with  additional 
current  from  the  line.  To  make  the  series  motor  available  for 
this  kind  of  braking,  and  to  return  energy  to  the  constant-poten- 
tial trolley  circuit,  it  is  necessary  to  add  a  shunt  field.  This 
complicates  the  construction  of  the  motor  and  of  the  controller 
to  a  point  where  it  is  not  ordinarily  considered  feasible. 

It  is  possible  to  short-circuit  the  motor  on  itself,  after  the  line 
circuit  has  been  disconnected.  In  this  case  the  machine  acts 
as  an  ordinary  series  generator,  and  will  deliver  a  current  de- 
pendent on  its  characteristic  and  the  resistance  in  the  external 
circuit.  By  properly  choosing  the  resistance,  the  power  delivered 
can  be  adjusted  as  desired,  with  a  corresponding  retardation 
of  the  train. 

To  adapt  this  method  of  braking  to  a  set  of  motors  with  series- 
parallel  control,  it  is  necessary  to  reverse  the  motor  fields  so  the 
e.m.f.  will  be  generated  in  the  proper  direction.  The  resistance 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     197 

may  be  chosen  to  give  the  desired  retardation.  This  is  a  method 
of  emergency  braking  which  is  always  available  on  any  car 
equipped  with  two  or  more  motors  and  series-parallel  control. 
The  machines  may  be  disconnected  from  the  line,  reversed 
and  thrown  to  the  parallel  position.  They  will  then  generate 
e.m.f.'s  in  the  same  direction;  but,  since  the  magnetic  circuits  are 
never  absolutely  identical,  there  will  be  more  residual  magnetism 
in  one  or  the  other  machine,  so  that  it  will  overpower  the  other 
and  operate  it  as  a  motor.  The  two  e.m.f.'s  will  then  be  in  series, 
and  a  considerable  current  will  flow  around  the  local  circuit,  whose 
value  will  be  determined  by  the  speed  of  the  car  and  the  resist- 
ance. The  power  required  for  this  action  is  taken  from  the 
momentum  of  the  car,  and  tends  to  reduce  the  speed.  In  the 
case  of  a  four-motor  equipment,  with  the  ordinary  platform  con- 
troller, it  is  unnecessary  to  throw  the  handle  to  the  parallel 
position,  for  the  pairs  of  motors  are  placed  in  parallel  through  the 
reverser.  All  that  is  needed  is  to  change  the  connections  by 
throwing  the  reverse  lever.  It  is  obvious  that  if  the  car  is  moving 
backward,  the  braking  effect  will  be  produced  with  the  controller 
thrown  to  the  forward  position. 

With  some  types  of  controller  the  only  resistance  will  be  that 
of  the  motors  and  the  wiring,  so  that  the  current  and  the  braking 
effort  will  be  large,  but  if  the  method  is  used  for  emergency  stops 
only,  this  will  not  occasion  any  difficulty.  If  the  torque  de- 
veloped is  so  great  as  to  cause  the  wheels  to  slide,  the  e.m.f. 
generated  by  the  motors  falls  to  zero,  and  the  torque  conse- 
quently disappears.  The  motors  will  then  revolve,  again 
producing  a  braking  effort. 

Newell  Magnetic  Brake. — A  form  of  brake,  depending  on 
the  same  principle,  but  using  it  much  more  effectively,  was 
developed  about  ten  years  ago,  and  placed  on  the  market  under 
the  name  of  the  "Newell"  brake,  from  its  inventor.  In  this  type, 
shown  in  Fig.  94,  the  current  from  the  motors,  acting  as  gen- 
erators, is  passed  through  the  coil  a  of  the  magnet,  6,  pulling  it 
against  the  track  and  providing  a  powerful  braking  effort.  The 
movement  of  the  magnet  downward  has  also  the  effect  of  operat- 
ing the  lever  system,  thus  applying  the  brake  shoes  to  the  wheels. 
The  effect  of  the  magnets  is  twofold;  in  addition  to  producing  a 
braking  effort  in  themselves,  they  pull  the  entire  truck  down  on 
the  track  with  increased  force  so  that  a  greater  total  braking 
effort  may  be  applied  to  the  wheels. 


198  THE  ELECTRIC  RAILWAY 

An  ingenious  feature  of  the  Newell  brake  is  that  the  energy 
wasted  in  resistance,  instead  of  being  dissipated  to  the  air  be- 
neath the  car,  is  utilized  for  heating  by  having  the  resistors  put 
inside  the  car  body  in  place  of  the  ordinary  electric  heaters. 
Both  the  loss  at  starting  and  while  braking  are  used  to  heat 
the  resistors;  and  the  material  of  which  they  are  made  is  such 
as  to  store  the  heat  and  give  it  out  at  a  nearly  uniform  rate. 
With  city  cars  making  frequent  stops,  the  amount  generated  in 
this  manner  is  ordinarily  more  than  sufficient  to  keep  the  tem- 
perature as  high  as  is  usual  with  the  ordinary  methods  of  heat- 
ing. While  there  is  no  reason  why  the  starting  loss  should  not 
be  used  in  the  same  way,  when  this  system  of  braking  is  not 
employed,  it  is  not  customary  to  do  so.  For  service  in  summer 


FIG.  94. — Newell  electromagnetic  brake. 

Current  delivered  by  the  car  motors  acting  as  generators  is  passed  through  the  coil  a  of 
the  electromagnet  b,  causing  a  braking  effort. 

a  duplicate  set  of  resistors  is  placed  beneath  the  car  in  the  usual 
position. 

With  this  type  of  brake  it  is  entirely  practical  to  obtain  retar- 
dations of  3  miles  per  hr.  per  sec.  and  over.  The  greatest 
operating  difficulty  with  the  Newell  brake,  as  with  all  types 
utilizing  the  motors  to  generate  current  in  a  local  circuit,  is  that 
when  the  rotation  of  the  wheels  ceases  the  braking  effort  stops. 
It  is,  therefore,  necessary  to  use  the  hand  brake,  or  some  other 
form  of  power  brake,  to  hold  the  train  after  it  has  been  brought 
to  rest,  which  is  an  undesirable  feature.  Another  objection  is 
that  the  motors  are  working  a  greater  portion  of  the  time,  so  that 
the  effective  heating  (r.m.s.)  current  is  increased.  If  they  are 
of  more  than  sufficient  capacity  to  make  the  schedule,  this  will 
have  but  little  effect;  but  if  already  worked  to  the  heating  limit, 
the  imposition  of  the  added  load  will  force  them  beyond  their 
continuous  capacity  and  cause  damage.  This  point  should  be 
given  careful  study  in  case  any  such  form  of  brake  is  to  be 
applied. 


BRAKING  OF  ELECTRIC  RAILWAY  TRAINS     199 

Momentum  Brakes. — The  inertia  of  the  train  may  also  be 
used  to  operate  a  mechanical  brake.  Momentum  brakes  have 
been  designed  in  which  the  shoes  or  drums  are  brought  in  con- 
tact by  means  of  some  form  of  friction  clutch.  This  type  has 
never  been  very  successful,  and  its  use  has  been  extremely  limited. 
It  is  difficult  to  make  any  such  form  of  brake  operable  for  more 
than  a  single  car,  which  limits  its  application  at  once.  It  is 
extremely  doubtful  whether  any  such  device  can  ever  find  a 
wide  use. 


CHAPTER  VIII 
CARS  AND  CAR  EQUIPMENT 

Classification. — Cars  for  railway  operation  may  be  very 
broadly  divided  into  two  main  groups:  those  for  freight  or  ex- 
press service  and  those  for  the  transportation  of  passengers. 
Cars  of  the  former  type  have  been  standardized  to  a  large  de- 
gree, and  their  design  must  conform  to  certain  rules  adopted  by 
the  Interstate  Commerce  Commission  and  the  Master  Car 
Builders'  Association.  Passenger  cars,  on  the  contrary,  are  not 
subject  to  such  rigid  supervision;  and,  especially  in  the  case  of 
electric  roads,  there  is  wide  divergence  in  their  design.  It 
is  with  those  of  the  latter  type  that  this  chapter  treats. 

The  development  of  car  design  for  electric  railway  service 
has  very  closely  followed  the  growth  of  the  different  classes  of 
roads,  as  enumerated  in  Chapter  I.  Passenger  cars  for  electric 
railways  may  therefore  be  roughly  classified  as  follows: 

1.  Cars  for  city  and  suburban  service. 

2.  Rapid  transit  cars  (elevated  and  subway). 

3.  Interurban  cars. 

4.  Trunk-line  coaches. 

5.  Special  service  cars. 

The  latter  two  types  need  not  differ  in  any  particular  from 
standard  cars  for  steam  railway  service.  On  such  trunk  lines 
as  have  been  or  may  be  electrified,  our  present  experience  indi- 
cates that  all  motive  power  will  be  supplied  by  independent 
locomotives,  so  that  no  electrical  equipment  on  the  cars  is 
needed  for  successful  operation.  In  case  a  general  electrification 
of  any  railroad  is  made,  it  may  be  desirable  to  include  such  minor 
details  as  electric  light  and  heat,  and  possibly  bus  lines  and 
control  cables  so  that  the  motive  power  may  be  subdivided 
and  placed  at  intervals  throughout  the  length  of  the  train, 
and  handled  with  multiple-unit  control.  Such  changes  are  of 
minor  importance,  and  need  not  be  considered,  since  they  do  not 
require  any  modification  of  the  design. 

200 


CARS  AND  CAR  EQUIPMENT  201 

Cars  of  the  types  for  operation  on  city  surface  railways 
("  tram  ways")  have  undergone  a  gradual  development  from 
the  same  beginnings  as  the  steam  railroad  coach;  but  the  neces- 
sities of  the  service  have  produced  a  radically  different  structure. 
Although  street  cars  have  been  passing  through  a  process  of 
evolution  for  the  last  60  years,  there  is  today  less  uniformity  in 
design  than  ever  before.  This  is  largely  due  to  the  changing 
conditions  of  operation  on  large  city  roads,  which  are  forcing 
them  to  provide  increased  facilities  and  at  the  same  time  receive 
less  return  on  the  investment.  In  order  to  meet  this  situation, 
car  builders  and  railway  companies  are  today  developing  radical 
designs  with  the  object  of  better  and  more  economical  operation. 

Since  they  run  almost  exclusively  on  private  right-of-way,  cars 
for  elevated  and  subway  service  are  not  subject  to  the  same 
limiting  conditions  as  to  size  and  weight  as  are  surface  cars. 
Their  design  approaches  more  nearly  that  of  standard  steam 
coaches.  The  main  difference  lies  in  the  fact  that  to  secure  rapid 
movement  the  doors  must  be  specially  designed  to  facilitate 
passenger  interchange. 

For  interurban  service  the  cars  may  be  quite  similar  to  standard 
railway  coaches.  Since  they  are  ordinarily  operated  in  one-  or 
two-car  trains,  it  is  often  essential  that  a  single  unit  combine  the 
functions  of  coach,  smoker,  baggage  car,  and  sometimes  express 
and  mail.  As  the  traffic  on  roads  of  this  class  is  largely  local, 
more  attention  should  be  paid  to  the  design  of  doors  than  in  cars 
for  through  trunk-line  traffic. 

Structural  Classification  and  Development. — Considering  cars 
from  a  structural  standpoint,  they  may  be  classified  according  to 
form  or  type,  to  material,  or  to  framing  and  construction. 
They  naturally  divide  themselves  into  two  types:  closed  or 
"box"  cars,  and  open  or  "summer"  cars. 

The  early  designs  of  street  cars  were  of  the  closed  body  or 
"box  car"  type;  and  most  of  the  more  recent  developments 
have  been  in  this  class.  The  first  cars  were  direct  adaptations 
of  the  stage  coach  for  service  on  railways  or  tramways.  While 
those  for  steam  roads  were  soon  increased  in  size,  and  before 
long  crystallized  into  standard  designs  of  considerable  capacity, 
the  street  cars,  due  to  the  limitations  of  animal  power,  tended 
toward  extremely  light  construction.  The  one-horse  "bobtail" 
car  was  the  first  development  for  purely  city  service.  Cars  of 
this  type  were  usually  about  12  ft.  long,  were  single  ended,  and 


202  THE  ELECTRIC  RAILWAY 

were  arranged  for  operation  by  one  man,  the  driver.  The  floor 
plan  of  a  car  of  this  type  is  given  in  Fig.  95.  With  the  growth  of 
cities  and  the  corresponding  development  of  the  street  railway 
business,  came  a  demand  for  designs  of  increased  capacity.  This 
led  to  the  construction  of  cars  of  about  18  to  20  ft.  length  of  body 
(Fig.  96),  usually  drawn  by  two  horses.  In  some  cases  these 
were  handled  by  the  driver  alone,  but  more  frequently  they 

were  arranged  for  two- 
man  operation.  Due  to 
.^  the  necessity  of  light 
weight,  no  further  de- 
velopment was  possible  so 


H— -  -  it' >i  long  as  animal  power  was 

FIG.  95.— Floor  plan— one  horse  car.        retained.     The  use  of  the 

This  type  of  car  was  in  use  in  a  large  number  of  cable  did  not  change  the 
American  cities  from  about  1850  to  as  late  as  1900. 

situation    to   any   extent, 

since  its  strength  was  limited,  and  the  car  weight  had  to  be 
kept  a  minimum. 

The  advent  of  electric  power  changed  the  entire  situation. 
Although  most  of  the  early  electric  cars  were  the  same  ones  that 
had  previously  been  used  with  horses,  it  was  almost  immediately 
seen  that  the  limit  to  size  had  been  removed.  A  gradual  increase 
began  at  once;  but  before  long  the  limit  of  capacity  for  a  single 


- -20   -- 

FIG.  96. — Single-truck  horse  car,  or  early  electric  car. 

A  later  model  than  that  shown  in  Fig.  95,  designed  to  be  drawn  by  two  horses.      Many  of 
them  were  remodeled  and  fitted  with  electric  motors  between  1890  and  1900. 

truck  caused  the  adoption  of  longer  bodies,  supported  by  two 
swiveling  or  " bogie"  trucks.  This  has  become  the  standard  for 
nearly  all  classes  of  service,  the  small  single-truck  car  having  now 
been  superseded  in  all  important  cities,  except  for  special  service 
or  on  lines  of  extremely  light  traffic. 

The  open  car,  Fig.  97,  has  always  been  a  favorite  with  the 
riding  public.  It  is  only  applicable  for  city  service,  being 
unsuited  for  high  speeds  or  for  long  runs.  It  usually  consists  of 


CARS  AND  CAR  EQUIPMENT 


203 


a  wooden  underframe,  supporting  a  skeleton  side  framing  with 
a  light  roof.  On  account  of  the  lack  of  side  bracing,  it  is  struc- 
turally weak.  The  seats  are  ordinarily  transverse  benches 
extending  the  entire  width  of  the  car,  and  access  is  obtained  by 
a  step  or  running  board  at  either  side.  Such  an  arrangement  is 
dangerous  for  the  passengers.  It  may  be  shown  that  it  is  slower 
to  load  and  unload  than  the  modern  types. 

While  the  open  car  may  be  justified  in  southern  climates,  where 
it  can  be  in  service  the  entire  year,  its  use  in  northern  cities  is 
limited  to  a  season  seldom  over  six  months  long.  This  requires 


FIG.  97. — Single-truck  open  car. 

This  type  of  car  has  been  in  use,  both  with  horses  and  with  electric  motors,  from  the  early 
days  of  street  railways  up  to  the  present  time. 

a  duplication  of  equipment.  Some  of  the  smaller  roads  reduce 
the  capital  expense  by  using  the  same  trucks  under  both  open 
and  closed  cars,  transferring  them  at  stated  dates.  This  prac- 
tice is  open  to  considerable  objection. 

In  order  to  meet  the  demand  for  the  open  car,  and  at  the 
same  time  reduce  the  total  cost  of  equipment,  a  new  type  was 
designed  about  ten  years  ago,  known  as  the  "convertible"  car. 
In  this  the  window  sash  and  side  paneling  could  be  removed  or 
else  stored  in  the  roof,  so  that  the  same  body  was  available 
for  either  summer  or  winter  service.  Due  to  the  inherent 
structural  weakness  and  the  difficulty  of  getting  a  tight  con- 
struction for  winter  service,  this  car  never  had  a  great  popularity 
with  the  street  railways. 

A  compromise  between  the  closed  and  the  open  types  was 
finally  made  in  the  so-called  " semi-convertible'7  car.  This  is 


204  THE  ELECTRIC  RAILWAY 

practically  a  closed  car,  but  with  larger  windows  than  ordinary. 
The  sash  are  either  stored  in  the  roof  or  in  pockets  in  the  side 
walls  beneath  the  window  sill.  With  the  use  of  transverse  seats, 
this  type  meets  most  of  the  demands  of  the  riding  public,  and 
is  adaptable  to  any  of  the  methods  of  fare  collection  which  have 
become  standard  in  the  last  few  years. 

In  the  larger  cities,  the  demand  for  units  of  very  great  capacity 
has  become  pressing  in  the  past  few  years.  Double-truck  cars 
of  the  largest  types  have  been  unable  to  meet  the  needs  where 
street  congestion  is  great.  At  the  present  time,  several  cities 
are  making  experiments  with  double-deck  cars  to  obtain  maximum 
capacity  with  minimum  space  in  the  street.  These  have  not  been 
in  service  for  a  sufficient  length  of  time  to  demonstrate  their 
worth,  but  it  is  probable  that  their  use  will  be  extended  where 
congestion  is  a  maximum. 

Another  attempt  to  increase  capacity  has  been  made  by  the 
use  of  articulated  cars.  In  the  types  which  have  been  brought 
out,  two  small  car  bodies  have  their  platforms  removed  and 
are  joined  by  a  flexible  unit,  so  that  the  combination  forms  a 
single  car.  The  entrance  is  placed  in  the  flexible  platform,  and 
the  exits  are  at  the  ends.1 

Still  another  method  for  getting  increased  car  capacity  is  the 
use  of  trains  of  two  or  more  units.  These  may  consist  of  one 
motor  car  and  trailers,  or  two  or  more  motor  cars,  operated  by 
multiple-unit  control. 

Exceptional  'conditions  have  from  time  to  time  brought  forth 
special  designs  of  cars.  Among  these  may  be  mentioned  the 
" California"  type.  This  car  is  a  combination  of  closed  and 
open  car.  In  most  of  the  designs  the  center  portion  of  the 
body  is  enclosed  while  the  end  portions  of  the  car  are  open.  It 
is  a  favorite  where  the  climate  is  mild,  but  is  changeable,  as  in 
California.  It  is  not  likely  to  ever  have  a  very  wide  field  of 
application,  since  in  localities  where  the  weather  changes  are 
sudden  and  severe  the  car  has  practically  one-half  its  capacity 
idle  at  all  times. 

Materials  of  Car  Construction. — All  the  earlier  cars  for  every 
class  of  service  were  built  exclusively  of  wood.  This  is  the 
cheapest  available  material,  and  its  fabrication  does  not  call  for 
expert  design.  Within  the  last  ten  years  the  price  of  wood  has 

1  For  a  more  complete  description,  see  Electric  Railway  Journal,  Vol. 
XLI,  p.  583;  Mar.  29,  1913. 


CARS  AND  CAR  EQUIPMENT  205 

risen  considerably,  so  that  the  advantage  of  low  cost  is  less 
than  formerly.  Steel  as  a  material  for  cars  has  been  making 
rapid  progress,  for,  although  the  first  cost  is  greater,  the  de- 
preciation is  less.  Steel  cars  are  more  reliable  and  are  nearly 
free  from  fire  risk.  In  collisions  they  stand  up  better  than  those 
built  of  wood.  The  advantages  of  wood  as  an  interior  finish 
are  obvious;  and  some  roads  seek  to  retain  the  good  points  of 
both  materials  by  adopting  a  semi-steel  construction,  in  which 
the  main  framing  is  of  steel,  the  details  and  finish  being  of 
wood.  This  makes  a  cheaper  structure  than  the  all-steel  car, 
but  the  fire  risk  is  greater  and  the  depreciation  usually  more. 
The  use  of  the  all-steel  car  is  increasing  rapidly,  and  it  is  quite 
possible  that  it  will  be  required  by  law  on  all  main  line  passenger 
roads  within  a  few  years. 

Framing. — There  are  three  general  methods  of  supporting 
the  car  body.  The  oldest  and  most  used  is  to  build  a  heavy 
underframe  or  platform,  which  is  strong  enough  and  sufficiently 
rigid  to  carry  the  entire  superstructure.  This  construction  pro- 
duces a  very  satisfactory  car,  whether  the  framing  is  of  steel  or 
of  wood,  but  it  is  often  unnecessarily  heavy  and  correspondingly 
costly.  The  expense  incident  to  hauling  needless  dead  weight 
may  be  a  large  amount  on  a  road  operating  many  cars;  and 
the  framing  should  be  so  designed  as  to  reduce  this  extra  weight 
to  a  minimum.  This  can  be  done  by  carefully  determining  the 
stresses  in  all  parts  and  designing  the  members  only  sufficiently 
heavy  to  give  a  proper  factor  of  safety.  When  the  entire  strength 
is  in  the  floor  or  bottom  framing,  the  vertical  stiffness  is  not 
great,  and  must  be  supplied  either  by  making  the  longitudinal 
members  heavy,  or  by  providing  tension  members  beneath  the 
sills. 

A  second  method  of  framing  was  invented  by  George  Gibbs, 
and  first  used  in  the  design  of  the  original  steel  cars  for  the  New 
York  subway.1  The  principal  difference  in  this  design  is  that 
the  main  longitudinal  members  are  located  at  the  top  of  the 
car,  the  weight  being  carried  by  the  sills  through  the  medium  of 
the  window  posts.  The  floor  framing  is  light,  having  only  enough 
strength  to  support  itself.  The  window  posts  are  heavy  enough 
to  transmit  the  load  to  the  bolsters.  By  the  adoption  of  this 
construction,  the  total  weight  of  the  members  may  be  less  than 

1  A  complete  description  of  the  original  subway  cars  is  given  in  American 
Engineer  and  Railroad  Journal,  October,  1904. 


206  THE  ELECTRIC  RAILWAY 

with  the  rigid  underframe.  It  is  obvious  that  this  is  only  appli- 
cable to  cars  built  wholly  or  partially  of  steel;  but  with  this  type 
of  framing  they  may  be  made  nearly  as  light  as  those  of  wood. 

A  third  method  of  construction  makes  the  side  sheathing 
of  the  car  furnish  a  large  portion  of  the  vertical  stiffness,  the  de- 
sign being  quite  similar  to  the  familiar  plate  girder  bridge.  By 
thus  utilizing  the  side  sheathing,  a  maximum  weight  efficiency 
may  be  obtained.  Cars  of  this  type  have  been  designed  for  a 
considerable  number  of  city  roads,  for  a  few  interurbans,  and  for 
nearly  all  of  the  elevated  and  subway  lines.  The  excellence  of 
this  framing,  and  the  comparatively  small  amount  of  dead  weight, 
is  increasing  its  popularity;  so  that  it  is  likely  to  become  stand- 
ard for  many  types  of  cars  for  different  classes  of  service. 

Roof  Framing. — In  the  early  designs  of  cars,  the  roofs  were 
made  independent  of  the  bodies,  and  were  of  the  lightest  con- 
struction, often  being  flimsy.  Operation  by  electric  power 
with  an  overhead  trolley  made  it  necessary  to  considerably 
strengthen  the  roof  framing.  At  the  same  time,  it  was  felt  that 
the  flat  roof  design  of  the  old  standard  horse  car  did  not  permit 
good  ventilation.  A  somewhat  radical  change  was  made  by  the 
addition  of  the  ''monitor  deck,"  the  type  which  is  familiar  on 
steam  railroad  coaches.  After  a  long  period  of  use,  it  has  been 
found  that  the  monitor  roof,  with  movable  sash,  does  not  offer  a 
satisfactory  solution  of  the  ventilation  problem,  and  that  the 
break  in  the  roof  framing  inherent  to  the  design  makes  a  weak 
structure.  Ventilation  has  been  taken  care  of -by  various  systems, 
some  dependent  on  the  motion  of  the  car  to  draw  the  used  air 
out  through  special  ventilators,  while  in  others  air  is  circulated 
by  means  of  motor-driven  blowers.  The  application  of  these 
devices  has  removed  the  primary  need  for  the  monitor  deck;  and 
the  secondary  purpose,  to  furnish  light,  has  been  all  but  defeated 
through  the  use  of  colored  glass. 

A  solution  of  the  roof  problem  which  has  been  satisfactory 
was  advanced  a  few  years  ago,  and  is  being  adopted  in  many  of 
the  new  designs.  The  monitor  is  omitted  entirely,  the  roof 
being  made  in  the  form  of  a  flat  arch,  rounded  at  the  ends  to  form 
a  platform  hood.  The  use  of  steel  angles,  bent  to  the  proper 
shape,  for  carlines,  results  in  stiffening  the  roof  to  a  marked 
degree,  and  with  a  reduction  in  weight  over  the  monitor  design. 
The  natural  lighting  of  the  car  need  not  be  interfered  with,  since 
the  form  of  the  roof  allows  the  windows  to  be  made  somewhat 


CARS  AND  CAR  EQUIPMENT  207 

higher.  A  further  development  is  to  continue  the  window  posts 
upward,  bending  them  in  a  complete  arch,  and  making  them 
serve  for  carlines.  This  still  further  strengthens  the  framing, 
making  the  entire  structure  more  nearly  one  complete  unit. 

In  any  of  the  arch-roof  cars  the  ventilation  must  be  taken  care 
of  by  some  form  of  forced  air  circulation.  Careful  design  has 
given  much  better  results  in  this  respect  than  were  possible  with 
the  monitor  roof;  and  the  general  appearance  of  the  car,  both 
interior  and  exterior,  is  at  least  as  good  as  that  of  the  earlier 
type. 

Door  Arrangement. — Where  the  stops  are  infrequent,  as  in 
trunk-line  service,  the  arrangement  of  the  car  interior  is  generally 
for  the  comfort  of  the  passengers  during  the  journey,  any  extra 
time  consumed  at  stops  being  of  minor  importance.  With  city 
surface  lines  and  rapid  transit  roads,  however,  the  main  object 
is  to  obtain  a  fair  schedule  speed  with  a  maximum  number  of 
stops.  In  such  cases  the  length  of  ride  per  passenger  is  compara- 
tively short,  and  a  certain  amount  of  comfort  may  be  sacrificed 
in  order  to  reduce  the  duration  of  the  trip.  For  this  class  of  traffic 
the  arrangement  of  the  car,  both  as  regards  the  seating  and  the 
doors,  should  be  made  to  facilitate  the  movement  of  passengers 
when  entering  and  leaving.  The  earliest  types  of  car  for  this 
service  were  on  the  same  general  plan  as  the  ordinary  steam 
coach,  having  doors  at  each  end,  and  seats  arranged  either  trans- 
versely, or  longitudinally,  as  in  Fig.  96.  In  the  older  cars,  the 
platforms  were  entirely  open ;  but  owing  to  public  demands,  most 
of  them  have  been  enclosed  with  permanent  vestibules  for  the 
past  ten  years.  The  first  effect  of  this  change  was  to  attract  a 
large  number  of  passengers  to  the  platforms,  where  they  rode  by 
preference.  Naturally  this  tended  to  congest  the  entrances,  and 
to  make  rapid  loading  and  unloading  difficult.  In  some  cities, 
such  use  of  the  platforms  by  passengers  has  been  prohibited. 
Although  this  aids  to  some  extent  it  still  is  not  the  best  arrange- 
ment for  rapid  interchange.  A  simple  expedient  is  to  use  one 
end  of  the  car  for  entrance  only,  and  the  other  for  exit.  This 
establishes  regular  paths  for  the  movement  of  the  passengers,  and 
aids  greatly  in  reducing  the  time  of  stops.  Many  objections  to 
this  method  of  operation  have  been  raised,  the  principal  one  being 
that  passengers  must  either  get  on  or  off  the  car  quite  a  distance 
from  the  street  crossing,  which  may  necessitate  walking  through 
mud  or  snow.  In  some  cities  a  compromise  is  made  by  regularly 


208 


THE  ELECTRIC  RAILWAY 


employing  the  scheme  mentioned  above,  but  allowing  passengers 
to  use  either  platform  as  an  exit  at  the  discretion  of  the  con- 
ductor. With  this  modification,  the  efficiency  of  the  method  is 
reduced  considerably. 

The  proper  design  and  location  of  the  entrance  and  exit  doors 
has  a  marked  effect  on  the  rapidity  of  loading  and  unloading. 


r 

^> 

L.      ' 

-  i                i 

FIG.  98. — Accelerator  car. 

An  early  attempt  to  prevent  crowding  of  the  entrance  and  exit,  and  to  reduce  the  time  of 
stops.     Suitable  for  single-end  operation  only. 

The  single,  narrow  swinging  door  of  the  steam  coach  limits  the 
speed  with  which  passengers  can  enter  or  leave  the  car.  If  doors 
of  this  type  are  used  for  street  cars,  a  long  time  will  b,e  needed  at 
stops.  An  early  attempt  to  aid  the  passenger  distribution  is  the 

— r 


FIG.  99. — Semi-accelerator  car. 
A  modification  of  the  type  shown  in  Fig.  98,  arranged  to  allow  double-end  operation. 

Brownell  "  accelerator "  car,  shown  diagrammatically  in  Fig.  98, 
In  this  the  doors  were  placed  at  one  side  of  the  center,  nearest  the 
entrance  step.  This  prevented  any  persons  who  might  be  stand- 
ing on  the  platform  from  interfering  with  the  movement  of  pas- 


Q 


D 


FIG.  100. — Center-door  car. 

A  recent  type  which,  with  a  few  minor  modifications,  has  been  adopted  in  a  number  of 
large  American  cities. 

sengers  boarding  the  car.  Such  a  design  is  only  applicable  where 
the  cars  always  run  in  one  direction.  Where  they  must  run 
either  way,  the  "semi-accelerator"  car,  Fig.  99,  could  be 
substituted. 

As  a  further  aid  to  rapid  movement,  center  doors  may  be  used, 
either  alone,  as  in  Fig.  100,  or  in  conjunction  with  the  end  doors. 


CARS  AND  CAR  EQUIPMENT 


209 


The  former  possess  many  practical  advantages,  due  to  the  fact 
that  the  passenger  movement  may  always  be  under  the  eye  of  the 
conductor,  and  he  may  be  held  responsible  for  any  accidents.  The 
great  operating  objection  to  the  center-door  car  is  that  it  is  more 
difficult  to  establish  regular  paths  for  the  passengers  than  in  the 
end-door  cars.  By  careful  training  of  the  conductors  it  is  possible 
to  largely  prevent  this  trouble. 

Seating  Arrangement. — The  influence  of  the  seating  plan  on 
the  rapidity  of  loading  and  unloading  is  quite  marked.     The  older 


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FIG.  101. — Cross-seat  car. 

A  design  widely  used  about  1900;  an  adaptation  from  steam  railroad  coach  designs. 

types  of  street  cars  were  nearly  all  equipped  with  longitudinal 
seats  on  either  side  of  the  center  aisle,  running  the  entire  length 
of  the  car  body  (Figs.  95,  96,  98,  99).  While  this  plan  is  fairly 
satisfactory  when  there  is  no  crowding,  it  becomes  bad  with  a 
standing  load.  It  is  unplesant  for  the  seated  passengers,  and 
inconvenient  for  those  standing.  The  use  of  transverse  seats, 
as  in  Fig.  101,  provides  greater  comfort  for  the  former,  but 


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FIG.  102. — Modified  type  of  cross-seat  car. 

A  development  from  the  design  shown  in  Fig.  101,  to  overcome  objectionable  crowding  at 
the  doors,  and  to  permit  of  a  wider  opening. 

restricts  the  amount  of  space  available  for  the  latter.  The  stand- 
ing space  is  more  comfortable  than  with  longitudinal  seats,  since 
grab  handles  may  be  placed  on  the  seat  backs  for  support.  The 
worst  trouble  is  that  the  congestion  near  the  entrance  and  exit 
doors  is  much  greater  than  with  side  seats.  A  compromise  is 
usually  adopted  in  city  cars  by  having  longitudinal  seats  near 
the  doors,  and  cross  seats  in  the  center  of  the  car,  when  designed 
for  end  entrance,  as  in  Fig.  102.  With  center  entrance  cars  the 


210  THE  ELECTRIC  RAILWAY 

trouble  is  not  so  marked,  and  the  seats  can  all  be  placed  trans- 
versely without  much  danger  of  congestion.  Other  combina- 
tions may  be  made  advantageously  for  particular  cases. 

A  more  logical  study  of  both  seating  arrangements  and  door 
design  has  been  made  in  conjunction  with  the  prepayment  of 
fares.  The  further  consideration  of  both  these  topics  will  be 
taken  up  in  that  connection. 

Fare  Collection. — Certain  roads,  especially  rapid  transit  lines, 
collect  fares  before  the  passengers  enter  the  cars.  This  obviates 
any  need  of  conductors,  guards  or  brakemen  being  the  only 
employees  needed  on  the  trains  in  addition  to  the  mot  or  men. 
Practically  all  surface  roads,  both  city  and  interurban,  are  so 
situated  that  fares  must  be  collected  after  the  passengers  have 
boarded  the  car.  According  to  the  older  methods,  the  conductor 
passed  through,  collecting  fares  from  passengers  after  they  had 
entered  and  become  seated.  Often  he  would  be  in  the  interior 
doing  this  during  a  stop.  This  practice  has  two  disadvantages: 
the  conductor  is  not  in  a  good  position  to  know  whether  the  steps 
are  clear  before  signaling  the  motorman  to  start,  nor  can  he  see 
the  passengers  who  are  entering  or  leaving  the  car.  Besides  mak- 
ing operation  dangerous,  this  makes  fare  collection  difficult,  and  in 
some  cases  almost  impossible.  It  also  gives  dishonest  conductors 
a  chance  to  "miss"  fares,  or  to  fail  in  registering  them.  A 
number  of  schemes  to  make  fare  collection  easier  and  more  cer- 
tain, and  to  reduce  accidents,  have  been  tried  within  the  past  few 
years.  Of  the  various  ones  advocated,  the  prepayment  plan 
has  met  with  the  most  success  in  the  United  States.  It  has  been 
adopted  in  nearly  every  large  city  in  the  country,  and  in  many  of 
the  smaller  ones.  The  basic  principle  of  all  methods  of  fare 
prepayment  is  to  have  the  conductor  at  or  near  the  entrance,  and 
to  prevent  any  person  from  going  into  the  car  without  first 
tendering  his  fare.  By  this  means  the  conductor  does  not  have 
to  depend  on  his  memory  to  ensure  collection  of  fares ;  and  he  may 
be  located  in  such  a  position  that  he  can  be  sure  the  steps  are  clear 
before  giving  the  signal  to  go  ahead.  In  the  later  types  of  pre- 
payment cars,  various  forms  of  doors,  operated  by  the  conductor 
from  his  fixed  position,  make  it  impossible  for  passengers  to 
enter  or  leave  after  the  starting  signal  has  been  given.  This 
reduces  the  boarding  and  alighting  accidents  by  a  marked 
degree. 


CARS  AND  CAR  EQUIPMENT  211 

If  the  fares  were  collected  at  the  instant  of  boarding  the  car,  the 
time  taken  in  loading  would  be  materially  increased.  This  is 
obviated  by  using  the  entrance  platform  for  holding  a  certain 
number  of  passengers  while  they  are  getting  their  fares  ready  to 
present  to  the  conductor,  the  door  being  closed  and  the  car 
started  immediately  after  they  have  boarded  the  platform.  In 
some  of  the  types  of  prepayment  cars,  as  many  as  ten  to  twelve 
passengers  may  be  accommodated  in  this  manner,  so  that  no  more 
time  is  consumed  in  the  ordinary  stop  than  where  fare  collection 
is  made  in  the  old  way. 

Types  of  Prepayment  Cars. — Practically  any  standard  type  of 
car  may  be  arranged  for  fare  prepayment.  The  success  of  any 
particular  design  depends  to  a  considerable  degree  on  the 
amount  of  space  available  for  passengers  before  presenting  fares. 
This  requires  special  design  of  platforms  in  most  cases. 


FIG.   103. — Original  Pay-As-You-Enter  car. 

The  conductor  is  stationed  in  the  fixed  position  shown,  and  receives  the  fares  from  the 
passengers  as  they  pass  him  on  entering  the  car.  The  seating  arrangement  is  not  an  essential 
feature  of  this  type  of  car. 

The  first  type  of  prepayment  car,  which  was  introduced  in 
Montreal  in  1905,  is  shown  diagrammatically  in  Fig.  103.  In  this 
the  platforms  are  lengthened  somewhat  from  the  standard  de- 
sign, and  a  railing  divides  the  rear  one  into  two  portions,  one  for 
entering  passengers,  and  the  other  for  the  conductor  and  leaving 
passengers.  The  conductor  remains  in  his  position  at  all  times, 
and  each  passenger,  on  entering  the  car,  tenders  his  fare  or 
deposits  it  in  a  special  fare  box.  The  conductor  is  then  in  a 
position  where  he  can  collect  all  fares,  and  where  he  can  watch 
the  movements  of  the  entering  and  leaving  passengers.  The 
front  door  is  used  for  exit  only,  and  is  under  the  observation 
of  the  motorman. 

In  the  original  design,  the  steps  were  not  movable,  and  no  en- 
closing doors  for  the  vestibules  were  provided.  No  special  at- 
tempt was  made  to  prevent  passengers  from  leaving  or  boarding 
the  car  while  in  motion.  Although  this  type  considerably  re- 


212  THE  ELECTRIC  RAILWAY 

duced  the  number  of  accidents  from  such  causes,  it  did  not  en- 
tirely prevent  them. 

Another  type  of  prepayment  car,  known  as  the  "Pay- Within" 
car,  was  brought  out  soon  after  the  "  Pay-As- You-Enter  "  car,  but 
by  a  rival  concern.  In  the  original  form,  shown  in  Fig.  104,  the 
bulkheads  are  entirely  removed,  the  conductor  is  stationed  in  the 
middle  of  the  end  entrance,  and  provided  with  an  operating 
stand.  The  vestibule  has  sliding  doors  which  are  worked  either 
by  compressed  air  or  by  a  system  of  hand-operated  levers,  worked 
from  the  operating  stand.  The  outside  steps  are  also  arranged 
to  fold  up  and  disappear  when  the  vestibule  doors  are  closed. 
In  this  design  the  entire  platform  is  made  available  for  entering 
passengers  waiting  to  pay  their  fares.  Exit  is  usually  made  by 


Conductor 


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FIG.   104. — Original  Pay- Within  car. 

A  type  developed  soon  after  the  P-A-Y-E  car.      The  principal  distinguishing  feature  is 
the  system  of  doors  and  folding  steps. 

the  front  platform,  the  door  being  the  same  as  that  for  entrance, 
but  controlled  by  the  motorman.  With  this  type  of  car  boarding 
and  alighting  accidents  are  practically  eliminated,  since  the  con- 
ductor is  instructed  not  to  give  the  starting  signal  until  the  en- 
trance door  is  closed;  and  the  motorman  must  not  start  the  car, 
after  receiving  the  signal,  unless  the  exit  door  is  closed.  The 
distinctive  feature  of  this  car  is  the  system  of  doors  and  folding 
steps. 

After  a  few  years  the  manufacturers  of  these  two  forms  of 
prepayment  cars  combined,  incorporating  the  good  features  of 
both.  Generally  speaking,  the  platform  construction  of  the 
original  P-A-Y-E  car  was  combined  with  the  door  arrangement 
of  the  Pay- Within  car,  producing  a  design  considerably  in 
advance  of  either. 

With  cars  of  the  prepayment  type,  it  is  essential  to  rapid  opera- 
tion that  the  space  near  the  doors  be  as  little  restricted  as  possible. 
For  this  reason  the  seating  arrangements  have  been  developed 
from  that  shown  in  Fig.  102,  since  in  most  cities  the  cross  seats 
have  been  found  more  desirable. 


CARS  AND  CAR  EQUIPMENT  213 

A  further  development  of  the  door-operating  principle  is  to 
have  the  doors  arranged  so  that  the  starting  signal  is  given  auto- 
matically when  all  of  them  are  closed.  This  may  be  accomplished 
very  simply  with  a  bell  or  light  circuit,  giving  the  indication 
to  the  motorman  without  signal  from  the  conductor.  The  scheme 
may  be  carried  still  further,  in  cars  equipped  with  multiple-unit 
control,  by  including  the  doors  in  the  master  control  circuit. 
With  this  arrangement  the  car  cannot  be  started  until  they  have 
all  been  closed.  It  then  becomes  possible  to  increase  the  speed 
of  operation,  for  as  soon  as  the  car  has  come  to  a  stop  and  the 
doors  have  been  opened,  the  motorman  can  throw  his  controller 
to  the  first  operating  position.  Then,  as  soon  as  they  have  been 
closed,  the  car  will  start  without  signals  of  any  sort  and  the 
motorman  can  at  once  turn  his  controller  further  as  desired.  If 
the  doors  are  opened  while  the  car  is  running,  power  will  imme- 
diately be  cut  off. 

Center  Entrance  Cars. — The  prepayment  principle  has  been 
extended  to  center  side-door  cars.  As  already  mentioned,  the 
side  door  has  many  operating  advantages.  It  decreases  the 
average  distance  the  passenger  must  go  from  the  entrance  to  find 
a  place;  and  since  the  platforms  are  unnecessary,  they  may  be 
entirely  omitted,  being  replaced  with  seats,  thus  adding  materi- 
ally to  the  capacity  of  the  car.  It  is  also  possible,  by  inclining  the 
floor,  to  make  a  car  with  lower  steps  than  the  standard.  In 
New  York,  a  design  has  been  produced  in  which,  by  having  the 
floor  inclined  upward  both  ways  from  the  center  door,  and  by 
the  use  of  special  features,  the  step  has  been  entirely  eliminated, 
the  car  floor  at  the  entrance  being  only  10  in.  above  the  street 
level1  (see  Fig.  105). 

Near-Side  Car. — A  special  type  of  car  has  been  designed  for 
prepayment  of  fares  in  connection  with  the  near-side  stop,  which 
is  being  required  in  many  cities  on  account  of  safety.  In  the 
" Near-Side"  car,  Fig.  106,  the  entrance  and  exit  are  both  on  the 
front  platform,  the  rear  platform  being  entirely  eliminated  un- 
less the  car  is  designed  for  double-end  service.  The  conductor 
is  relieved  of  all  operating  duties,  since  the  passengers  enter 
and  leave  the  car  under  the  eye  of  the  motorman.  The  latter, 
having  control  of  both  the  entrance  and  exit  doors,  can  start  the 
car  when  he  is  satisfied  that  the  steps  are  clear.  It  is  possible  to 

1  A  complete  description  of  this  car  may  be  found  in  Electric  Railway 
Journal,  Vol.  XXXIX,  p.  418,  Mar.  16,  1912. 


214 


THE  ELECTRIC  RAILWAY 


interlock  the  controller  with  the  doors,  so  as  to  prevent  opera- 
tion of  the  motors  unless  the  doors  are  closed.  The  conductor, 
then,  acts  merely  as  cashier,  his  function  being  to  make  change 
and  assure  himself  that  the  proper  fare  has  been  deposited  in  the 
fare  box  by  the  passenger.  In  small  cities  with  light  traffic,  the 


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FIG.  105. — New  York  stepless  car. 

The  floor  level  is  but  10  in.  above  the  ground,  and  there  are  no  steps  inside  the  car.  Note 
the  arrangement  of  seats  to  clear  the  pony  wheels,  and  the  position  of  the  motors  at  the 
outer  ends  of  the  trucks. 

conductor  may  even  be  dispensed  .with,  the  motorman  perform- 
ing the  duties  of  both.  In  the  latter  case,  the  time  consumed  in 
stops  is  liable  to  be  somewhat  longer  than  where  a  conductor  is 
employed. 


Conductor. 


Motorman 


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FIG.   106. — Near-side  car. 

The  entrance  and  exit  doors  are  under  the  control  of  the  motorman;  the  conductor  is  not 
required  tc  give  starting  signals. 

Rapid  Transit  Cars. — The  design  of  cars  for  service  on  elevated 
and  subway  roads  is  not  limited  as  for  use  on  surface  lines,  prin- 
cipally because  the  problem  of  fare  collection  does  not  enter.  In 
all  roads  of  this  class  prepayment  of  fares  is  an  essential  part; 
but,  on  account  of  the  physical  features,  making  it  possible  to 


CARS  AND  CAR  EQUIPMENT 


215 


operate  entirely  on  private  right-of-way,  payment  is  made  in 
the  stations  before  the  passengers  enter,  so  that  the  cars  can  be 
designed  entirely  for  comfort  and  rapidity  of  operation.  The 
doors  of  the  earliest  type  of  rapid  transit  car  were  modeled 
closely  after  those  of  the  open  platform  steam  coach  of  the 
same  period,  but  the  cars  ordinarily  had  longitudinal  seats  in- 
stead of  the  cross  seats  of  standard  railroad  designs.  Such  a 
car  is  shown  diagrammatically  in  Fig.  107. 


Cab    || 

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///^///////////^^^^ 

Fie.   107. — Early  rapid-transit  car. 

This  type,  with  open  platforms,  has  been  widely  used  on  all  of  the  earlier  elevated  roads. 
Note  the  position  of  the  motorman's  cab. 

It  is  to  be  noted  in  connection  with  all  cars  for  operation 
on  elevated  and  subway  lines  that,  since  the  platforms  must  be 
specially  designed  in  any  case,  there  is  no  advantage  in  having 
them  near  the  level  of  the  rail.  Much  more  rapid  loading  and 
unloading  can  be  obtained  with  them  at  the  level  of  the  car  floor, 
since  this  obviates  any  need  of  steps.  This  arrangement  also 
simplifies  the  car  framing  to  some  extent,  since  the  sills  can  be 
made  continuous  from  one  end  of  the  body  to  the  other. 


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FIG.  108. — Rapid-transit  car,  used  in  New  York,  Chicago,  Brooklyn,  etc. 

A  medication  of  the  open-platform  car  shown  in  Fig.  108. 

Another  type  of  rapid  transit  car,  shown  in  Fig.  108,  is  the  same 
in  general  design,  but  includes  a  few  cross  seats  near  the  middle  of 
the  car.  These  seats  are  invariably  of  the  non-reversible  type. 
Cars  such  as  shown  in  these  two  diagrams  have  been  operated 
on  the  principal  elevated  lines  for  many  years. 

The  general  demand  for  the  enclosed  vestibule  car  led  to  the 
type  shown  in  Fig.  109,  which  is  the  one  used  on  several  of  the 
elevated  lines  of  Chicago.  The  principal  operating  advantage 
in  this  design  is  that,  since  the  passengers  are  protected  from  the 


216 


THE  ELECTRIC  RAILWAY 


weather,  they  are  better  lined  up  at  the  exits  when  the  car  comes 
to  a  station. 

Since  the  principal  problem  in  the  design  of  rapid  transit  cars 
is  to  secure  swift  movement  of  the  passengers,  it  would  appear  that 
the  addition  of  doors  in  the  middle  of  the  sides  would  add  to 


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Ck 


FIG.  109. — Rapid-transit  enclosed  vestibule  car. 
A  later  type  than  those  shown  in  Figs.  107  and  108. 

the  speed  of  unloading  and  loading.  A  car  of  this  type,  shown  in 
Fig.  110,  was  first  used  on  the  Boston  Elevated  Railroad.  On 
that  road  the  scheme  is  to  have  the  passengers  enter  by  the  end 
doors  and  leave  by  the  center  doors.  If  this  plan  is  adhered  to 
by  all  the  passengers,  it  increases  the  rapidity  of  operation  con- 


flab                                                       N           U 

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FIG.   110. — Side-entrance  rapid-transit-car,  New  York. 

A  modification  of  the  type  shown  in  Fig.  109,  to  give  greater  facilities  for  rapid  loading 
and  unloading. 

siderably.  Unfortunately,  it  is  not  possible  to  completely  train 
the  American  riding  public  to  move  in  fixed  channels,  so  that  the 
advantage  of  establishing  regular  directions  of  movement  is  but 
partially  realized.  Even  a  partial  establishment  of  a  regular 


1 

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FIG.   111. — Side-entrance  rapid-transit  car,  Philadelphia. 

This  differs  from  the  New  York  car  principally  in  the  seating  arrangement. 

direction  of  motion  helps  to  some  extent;  and  it  would  seem  that, 
even  if  no  general  adherence  to  the  rule  were  made,  the  extra 
doors  should  aid  in  loading  and  unloading.  Cars  of  a  similar 
design  have  been  adopted  on  a  number  of  rapid  transit  roads. 


CARS  AND  CAR  EQUIPMENT 


217 


A  slight  modification  consists  in  the  addition  of  a  few  cross  seats 
on  either  side  of  the  center  doors,  as  shown  in  Fig.  Ill,  which 
represents  the  type  of  car  used  on  the  Philadelphia  elevated  road. 
Practically  the  same  results  in  rapidity  of  passenger  inter- 
change should  be  accomplished  by  combining  the  center  and  end 


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nmn 


umu 
nmn 


u 
n 


FIG.  112, — Rapid-transit  car,  Metropolitan  Railroad  of  Paris. 

Note  the  short  distance  from  the  doors  to  the  seats  in  any  part  of  the  car. 

doors,  placing  two  side  doors  some  distance  from  the  ends  of  the 
car,  as  in  Fig.  112,  which  represents  a  design  used  in  Paris.  In 
this  the  maximum  distance  from  a  seat  to  a  door  is  no  greater 
than  when  center  and  end  doors  are  used  in  a  car  of  equal  length. 


u  u — ' 
fi  n — i 


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an 


u 


FIG.  113. — Cambridge  subway  car. 

A  recent  type  of  rapid-transit  car,  arranged  for  large  capacity. 

A  movement  has  been  growing  in  the  past  few  years  for  longer 
cars  for  this  class  of  service,  since  the  passenger  capacity  can  be 
increased  to  some  extent  without  adding  to  the  platform  labor. 
Recent  cars  designed  for  the  Boston-Cambridge  subway  (Fig. 
113)  and  for  the  New  York  Municipal  Railway  (Fig.  114)  are 


nn 

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m, 


FIG.  114. — Rapid-transit  car,  New  York  Municipal  Railway. 

A  very  recent   car,  designed  after  a  comprehensive  study,  to  give  maximum  passenger 
capacity. 

examples  of  this.  In  both  types,  the  principle  mentioned  in  the 
last  paragraph  has  been  used  to  reduce  the  distance  from  the  doors 
to  the  seats;  but  both  cars  are  so  long  (69  ft.  6J£  in.  and  67  ft.  4 
in.,  respectively)  that  it  is  necessary  to  combine  these  side  doors 
with  center  side  doors,  as  used  in  some  of  the  earlier  designs.  In 


218  THE  ELECTRIC  RAILWAY 

this  way  the  distance  to  the  seats  is  no  more  than  in  the  end-  and 
side-door  cars;  and  is  actually  less  than  in  much  shorter  end- 
door  cars. 

While  it  is  desirable  to  seat  every  passenger,  it  is  generally 
recognized  that  in  congested  business  districts  it  is  not  possible 
to  provide  enough  cars  to  furnish  seats  for  all;  and,  when  many 
business  houses  close  at  the  same  time,  it  taxes  to  the  limit 
the  ordinary  rapid  transit  road  to  provide  accommodations  of  any 
kind.  This  has  been  recognized  in  the  car  for  the  New  York 
Municipal  Railway.  While  a  large  door  capacity  is  needed  for 
rush-hour  service,  it  is  not  so  necessary  at  other  times;  and  some 
of  the  doors  are  arranged  to  be  used  only  when  needed,  folding 
seats  being  placed  in  front  of  them  as  desired. 

The  effect  on  operation  due  to  the  use  of  different  rapid  transit 
cars  is  very  marked.  For  instance,  it  has  been  estimated  that  the 
new  New  York  Municipal  Railway  cars  will  increase  the  capacity 
of  the  track  by  20  to  25  per  cent,  over  what  it  would  be  if  the  latest 
type  of  cars  now  in  use  on  other  roads  of  its  class  in  New  York 
City  were  employed;  and  it  will  also  save  about  $200,000  a  year 
in  platform  costs,  and  between  $1,000,000  and  $2,000,000  in  power 
system  capacity  because  of  the  decreased  energy  consumption  per 
passenger  carried.1 

Interurban  Cars. — The  interior  arrangement  of  cars  for  inter- 
urban  roads  is  subject  to  more  conflicting  elements  of  design  than 
in  city  or  rapid  transit  service.  The  collection  of  fares  must  be 
considered  to  some  extent,  but  the  problem  is  not  so  serious  as  in 
city  cars;  for  the  number  of  passengers  entering  is  not  very  large 
at  any  one  stop,  and  the  rides  are  longer.  Further,  some  system 
of  fare  receipts  may  be  used  for  indemnification.  It  is  more  essen- 
tial to  provide  facilities  for  the  comfort  of  the  passengers,  and  this 
need  increases  with  the  average  length  of  ride.  On  roads  operat- 
ing trains  for  runs  exceeding  about  two  hours  in  length,  the  con- 
veniences should  be  about  the  same  as  those  standard  for  steam 
coaches.  A  car  which  has  been  adopted  by  one  of  the  larger 
interurban  roads  of  the  Middle  West  is  shown  in  Fig.  115.  In 
this  are  combined  the  functions  of  standard  passenger  coach, 
smoker,  and  baggage  car.  The  smoking  and  baggage  rooms  are 
merged,  in  order  to  save  space.  This  compartment  has  a  num- 
ber of  folding  seats  which  are  normally  used  for  passengers,  but 

1  See  Electric  Railway  Journal,  June  6,  1914,  Vol.  XLIII,  p.  1261. 


CARS  AND  CAR  EQUIPMENT 


219 


which  can  be  folded  back  against  the  walls  in  case  there  is  an 
extra  amount  of  baggage. 

The  use  of  the  center  entrance  car  for  interurban  service  has 
made  but  little  headway  so  far;  but  it  is  likely  to  have  a  wider 
application  in  the  future  on  account  of  its  excellent  qualities. 
The  main  compartment  may  be  separated  by  the  entrance  from 
the  smoking  and  baggage  rooms,  while  the  distance  from  any  part 
to  the  doors  may  be  reduced.  Fig.  116  shows  a  car  of  this  type 
which  has  been  successfully  used  in  high-speed  service. 


j      FoidingSeaf 

I Baggage, Exp.  and 

\  '"  |  Smoker 

v** .n 

\^          Folding  5e<rf     \ 


nnn 


u  u  u  u  u  u 
Hinnnn 


FIG.  115. — Standard  interurban  car,  Illinois  Traction  System. 

This  car  combines  all  the  features  of  the  ordinary  steam  railroad  local  passenger  train. 

A  number  of  interurban  roads  have  found  it  desirable  to  operate 
a  limited  freight  service.  To  do  this,  motor-equipped  cars  of 
the  ordinary  baggage  type  have  been  used.  In  some  cases  they 
are  operated  as  separate  units,  and  in  others  the  motor  capacity 
is  increased  so  that  they  are  able  to  haul  one  or  two  trailers. 

A  demand  has  been  found  for  interurban  parlor-car  service 
during  the  past  few  years;  and  to  satisfy  it,  cars  resembling  the 


uuuuu 

Smoker-  \ 

nnnnn 


Coach 


nnnnn 


FIG.  116. — Center-entrance  interurban  car,  Kansas  City,  Clay  County  and 
St.  Joseph  Railway. 

This  is  a  recent  design,  which  has  proved  quite  popular,  and  which  has  been  adopted  with 
minor  modifications  on  a  number  of  interurban  roads. 

Pullman  parlor  cars,  but  usually  shorter,  have  been  built.  These 
are  most  frequently  run  as  trailers  to  obviate  the  noise  incident 
to  motor  operation,  which,  although  slight,  is  objectionable  to 
some  patrons.  They  are  usually  a  source  of  considerable  revenue, 
for  they  furnish  additional  seating  capacity  which  is  paid  for  by 
the  excess  fares  charged. 

The  demand  for  dining  cars  on  electric  roads  has  been  very 
slight  up  to  the  present  time;  but  in  the  future,  if  several  roads 


220  THE  ELECTRIC  RAILWAY 

combine  to  give  through  service,  it  is  possible  that  a  need  for 
them  may  be  felt.  All  of  the  dining  service  now  handled  on 
interurban  roads  is  given  by  buffets  operated  in  conjunction  with 
the  parlor  cars. 

On  a  few  roads  it  has  been  desirable  to  run  night  trains  and 
to  supply  sleeping-car  service.  The  cars  which  have  been  used 
have  been  specially  designed,  and  include  a  number  of  features 
not  seen  on  the  standard  Pullman  cars.  Since  this  service  is 
entirely  special,  no  attempt  will  be  made  to  give  detailed  de- 
scriptions of  the  cars  used. 

Auxiliary  Electric  Devices. — Although  the  car  body,  the  motors 
and  the  control  are  the  essentials  of  the  rolling  stock,  a  large 
number  of  auxiliary  parts  are  needed  to  complete  the  equipment. 
Principal  among  these  are  the  lighting  devices  and  heating  sys- 
tem. While  neither  is  used  continuously  throughout  the  opera- 
tion of  the  car,  both  are  necessary  if  the  service  is  to  be  continued 
for  more  than  special  events. 

Car  Lighting. — Up  to  the  present  time,  the  lighting  of  electric 
cars,  both  for  city  and  for  interurban  service,  has  been  done  by 
clusters  of  16-c.p.  carbon  incandescent  lamps,  or  by  a  line  or 
lines  of  such  lamps  down  the  middle  or  sides  of  the  car.  They 
are  placed  five  in  series  on  the  trolley  circuit,  so  that  standard 
lamps  of  110  to  120  volts  may  be  used.  In  order  to  have  uni- 
formity in  illumination,  and  to  prevent  unequal  deterioration, 
the  lamps  must  be  carefully  matched  to  have  them  of  the  same 
current  capacity.  In  most  installations,  the  lamps  have  been 
left  bare,  or  provided  with  inadequate  shades  and  reflectors. 
Such  a  system  is  far  from  satisfactory,  for  the  amount  of  light 
produced  by  the  carbon  lamps  is  insufficient  for  reading,  while 
the  energy  consumption  is  high.  The  bare  lamps  are  not  ar- 
ranged for  the  best  distribution  of  the  light,  and  they  produce 
a  glare  in  the  eyes  of  the  passengers  which  is  harmful. 

Within  the  last  few  years  more  attention  has  been  paid  to  the 
correct  lighting  of  cars,  and  illuminating  engineers  have  put  a 
great  deal  of  thought  on  the  subject.  The  ordinary  car  is  a  diffi- 
cult interior  to  treat,  since  it  is  practically  a  long,  narrow  room, 
with  but  little  wall  space  for  diffusion  of  the  light,  and  with  a 
low  ceiling  which  is  usually  not  well  designed  for  reflection. 

The  first  step  in  the  improvement  of  car  illumination  is  the 
substitution  of  tungsten  lamps  for  the  carbon.  By  the  use  of 
23-watt  tungsten  lamps  in  place  of  the  50-watt  carbon  lamps, 


CARS  AND  CAR  EQUIPMENT  221 

the  lighting  cost  can  be  reduced  to  less  than  one-half,  while  the 
amount  of  light  is  increased  about  15  per  cent.  This  change 
has  been  made  in  a  number  of  large  city  roads. 

The  change  from  carbon  to  tungsten  lamps,  while  increasing 
the  total  amount  of  light,  does  not  get  rid  of  the  objectionable 
glare,  nor  does  it  improve  the  light  distribution.  More  recent 
developments  have  shown  that  by  the  use  of  fairly  large  units,  in 
the  neighborhood  of  100  watts,  spaced  much  further  apart  and 
equipped  with  proper  shades  and  reflectors,  the  total  amount  of 
light  in  the  car  may  be  somewhat  increased  and  its  distribution 
made  very  much  better.  This  is  also  accompanied  by  a  material 
reduction  in  energy  consumption  for  lighting,  less  cost  of  lamps, 
and  a  saving  in  the  necessary  wiring  for  the  car.  It  is  very  prob- 
able that  this  method  of  car  lighting  will  find  more  and  more  favor 
as  its  advantages  become  better  known.  The  principal  objection 
is  that  if  the  lighting  is  concentrated  in  five  units,  all  in  series,  a 
failure  of  one  lamp  will  throw  the  car  in  darkness.  This  can  be 
taken  care  of  by  the  use  of  a  selector  switch,  operated  by  the  con- 
ductor, by  means  of  which  a  spare  lamp  may  be  held  ready  to 
throw  into  the  circuit  in  case  of  another  burning  out.  It  is  prac- 
tically always  necessary  to  have  an  auxiliary  circuit  for  markers, 
destination  signs,  etc.,  and  one  or  two  lamps  on  this  circuit  can 
be  placed  in  the  car  interior  for  such  emergencies.  In  any  case 
it  is  easy  for  the  conductor  to  be  supplied  with  a  spare  lamp,  which 
can  be  used  to  replace  one  burned  out. 

One  general  objection  to  all  .lighting  systems  depending  on 
trolley  current  is  that  the  line  potential  is  liable  to  large  and  sud- 
den fluctuations.  While  these  have  but  little  effect  on  the  motor 
operation,  they  cause  flickering  of  the  lights,  often  to  such  an 
extent  as  to  make  reading  impossible.  This  condition  is  worse 
with  carbon  lamps,  and  is  considerably  improved  by  the  sub- 
stitution of  tungsten  lamps,  particularly  in  large  units.  But 
there  is  no  form  of  incandescent  lamp  which  will  stand  a  variation 
of  25  per  cent,  in  potential  without  a  wide  change  in  candle  power. 
Up  to  the  present  time,  no  remedy  has  been  seriously  suggested. 
One  method  which  has  been  tried  experimentally  consists  in 
placing  in  series  with  the  lamp  circuit  a  resistor  with  a  large 
positive  temperature  coefficient,  which  will  tend  to  steady  the 
lamp  potential.  This  has  not  been  put  in  practical  form,  and  in 
any  event  requires  the  waste  of  considerable  energy  to  be  effective. 
Another  suggestion  is  the  use  of  a  motor-generator  set  for  supply- 


222  THE  ELECTRIC  RAILWAY 

ing  the  lights.  This  is  also  open  to  the  objection  of  being  un- 
economical. With  trolley  potentials  of  1200  volts  and  over,  it 
becomes  a  necessity  to  use  some  such  device,  both  for  supplying 
the  lamps  and  furnishing  current  for  the  operation  of  the  control 
circuits.  This  gives  a  partial  solution  of  the  lighting  problem  on 
such  roads.  On  single-phase  roads,  the  variation  of  the  line 
potential  is  considerably  less,  and  the  lighting  troubles  are  not  so 
great,  as  on  the  low-potential  direct-current  lines. 

Car  Heating. — The  proper  heating  of  cars  in  winter  is  a  subject 
of  considerable  importance  in  northern  climates.  The  problem 
must  be  considered  from  a  number  of  different  angles,  and  is 
rather  difficult  of  solution  to  the  satisfaction  of  all  the  patrons  of  a 
road.  In  city  surface  cars,  the  passengers  usually  ride  for  short 
distances  and  keep  on  their  outer  clothing.  It  is  generally  suf- 
ficient to  keep  the  cars  heated  to  a  point  which  will  be  comfort- 
able to  persons  in  street  attire.  This  calls  for  interior  tempera- 
tures of  about  55°  to  60°  F.  For  suburban  and  interurban 
service,  where  the  average  ride  is  much  longer,  the  passengers 
usually  desire  to  remove  their  wraps.  In  this  case  the  tem- 
perature should  be  from  65°  to  70°  F. 

The  proper  heating  of  a  car  to  the  desired  temperature  is  in  it- 
self insufficient;  there  must  be  at  the  same  time  an  adequate  sup- 
ply of  fresh  air.  This  may  be  introduced  by  means  of  air  ducts  at 
the  front  end  of  the  car,  or  by  exhaust  ventilators  in  the  roof  or 
other  convenient  location.  In  order  to  get  the  air  warmed,  it 
should  be  passed  over  the  heaters  for  the  best  distribution. 

For  the  actual  generation  of  heat  there  are  available  at  least 
three  different  systems.  The  simplest  is  the  use  of  a  small  stove 
in  each  car,  placed  either  on  the  front  platform  or  in  some  con- 
venient location  inside.  This  arrangement  is  not  very  satis- 
factory, since  it  does  not  distribute  the  heat  uniformly  through 
the  car.  This  is  remedied  to  some  extent  by  placing  the  stove 
on  the  front  platform.  The  air  is  then  forced  over  it  before 
admission  to  the  car.  The  car  stove  is  in  any  case  dangerous  and 
dirty.  It  always  requires  attention,  even  though  that  may  be 
supplied  by  the  car  crew.  Its  principal  advantage  is  in  cheapness 
of  installation  and  operation. 

A  more  adequate  form  of  heating  is  made  by  the  use  of  hot  water 
as  a  circulating  medium,  it  being  heated  by  a  small  furnace  lo- 
cated at  some  convenient  point  in  the  car.  This  gets  rid  of  the 
uneven  distribution  of  heat,  and  thus  is  better  than  the  stove. 


CARS  AND  CAR  EQUIPMENT  223 

It  is  considerably  more  expensive  to  install,  costs  somewhat  more 
to  operate,  and  does  not  get  rid  of  the  danger  and  the  dirt  inci- 
dent to  the  use  of  a  coal  stove  on  the  car. 

The  third  type  of  heater  makes  use  of  electric  current  in  spe- 
cially designed  resistors.  These  may  be  located  at  convenient 
points  in  the  car,  usually  being  placed  under  the  seats  or  along  the 
side  walls.  The  distribution  of  heat  is  about  as  good  as  in  the 
hot-water  system.  The  heat  is  clean,  there  is  no  need  for 
attendance,  and  no  extra  fire  hazard  due  to  the  use  of  this  kind  of 
heaters.  Different  degrees  of  heat  may  be  obtained  by  subdivid- 
ing the  coils  of  the  resistors  as  desired.  It  is,  however,  more 
expensive  to  install  than  the  plain  stove,  but  somewhat  cheaper 
than  hot-water  heaters.  The  cost  of  operation  is  decidedly 
higher  than  for  the  other  types. 

On  city  roads  the  need  for  all  of  the  available  space  for  passen- 
gers, and  the  difficulty  of  the  train  crew  finding  time  to  care  for 
heaters,  practically  precludes  the  use  of  any  type  of  heat  but 
electric.  In  this  service  the  need  for  a  high  temperature  is  least, 
so  the  expense  of  operating  electric  heaters  is  less  than  for  the 
longer  runs.  In  some  cases,  electric  heat  may  even  be  found 
cheaper  on  long  runs  than  other  kinds. 

For  interurban  service,  the  use  of  electric  heaters  calls  for  a 
much  larger  expenditure  of  energy  than  on  city  roads.  The 
temperature  needed  is  greater,  and  the  high  car  speed  causes 
greater  losses  by  convection  currents  and  by  radiation.  For  most 
interurban  roads  the  hot-water  system  has  proved  the  most  satis- 
factory and  economical  of  any  type  of  heater. 

Electric  Heaters. — Electric  heaters  for  car  service  all  depend 
on  the  same  principle — the  dissipation  of  energy  in  resistance; 
and  since  the  energy  is  transformed  at  a  rate  equal  to  PR,  their 
electrical  efficiency  will  always  be  100  per  cent.  Mechanically, 
there  may  be  considerable  difference  in  heaters.  They  are  usu- 
ally made  of  resistance  wire  coiled  on  porcelain  forms,  and  their 
heat  storage  capacity  is  small.  Sudden  variations  in  the  trolley 
potential  will  therefore  cause  corresponding  rapid  fluctuations  in 
the  heat  produced.  Some  forms  are  made  with  the  embedded 
type  of  resistor,  in  which  the  heat  capacity  is  much  greater,  and 
the  distribution  is  more  uniform  than  with  the  plain  wire  type. 
On  the  other  hand,  it  takes  a  longer  time  to  warm  the  car  when 
the  heat  is  turned  on,  and  it  does  not  cool  so  rapidly  when  the 
current  is  cut  off. 


224  THE  ELECTRIC  RAILWAY 

Car  Wiring. — One  of  the  most  vital,  and  at  the  same  time  the 
most  vulnerable,  parts  of  the  car  equipment  is  the  main  power 
wiring.  Upon  it  depends  the  operation  of  the  motors  and  their 
proper  control.  It  is  essential  that  the  wiring  be  made  in  a  per- 
manent manner,  so  that,  in  spite  of  the  rough  handling  and  abuse 
incident  to  railway  service,  it  will  not  be  damaged. 

The  insulation  of  the  wiring  on  the  earliest  cars  was  extremely 
crude,  the  wires  being  installed  without  regard  to  arrangement, 
the  main  idea  being  to  operate  the  cars  in  some  fashion.  A  few 
years  later,  when  equipments  had  been  standardized  to  some 
extent,  regular  cables  were  made  up  of  the  requisite  number  of 
wires,  drawn  together  through  a  canvas  hose.  This  method  of 
wiring  was  used  with  considerable  success  for  a  number  of  years. 
There  was  always  danger  of  abrasion  of  the  insulation  and 
grounding  of  the  wires.  Finally  this  type  of  car  wiring  was 
superseded  by  later  and  better  methods. 

A  favorite  method  of  wiring  on  wooden  cars  is  to  install  the 
wiring  under  the  car,  the  individual  wires  being  insulated  for  the 
full  potential  and  being  held  to  the  framing  by  separate  wooden 
cleats.  This  leaves  the  wiring  open  for  inspection,  and  separates 
it  so  well  that  there  is  but  little  danger  of  grounds  and  short  cir- 
cuits. In  some  cases  the  open  construction  is  replaced  by  wiring 
run  in  metal  moulding.  This  gives  an  absolute  protection  against 
mechanical  injury. 

For  all-steel  cars  it  is  practically  imperative  that  the  wires  be 
run  in  conduit.  In  such  cases  it  is  agreed  that  the  best  practice 
is  to  bring  the  wires  out  through  standard  junction  boxes,  and 
fasten  them  to  the  car  underframing  with  asbestos  board  or  prop- 
erly treated  wooden  cleats,  which  are  arranged  to  allow  a  clear 
space  between  the  wires  of  at  least  2  in.1 

In  all  types  of  equipment,  it  is  necessary  to  provide  some  auto- 
matic protection  of  the  motors  against  overload.  The  ordinary 
method  is  to  use  fuses  and  circuit  breakers.  For  the  smallest 
equipments  fuses  are  used  alone,  but  their  employment  is  open 
to  a  number  of  operating  objections.  Generally  two  automatic 
circuit  breakers  are  placed  in  the  circuit,  one  at  each  end  of  the 
car.  In  some  cases  these  breakers  are  in  series,  while  in  others  one 
is  used  alone  at  each  end.  For  large  equipments  it  is  better  to 
have  both  the  circuit  breaker  and  the  fuse,  the  latter  being  set  to 

1  See  Engineering  Manual,  American  Electric  Railway  Association, 
Section  EC  lla. 


CARS  AND  CAR  EQUIPMENT  225 

open  at  a  slightly  higher  current  than  the  breaker,  so  that 
ordinarily  it  will  not  operate. 

Cars  for  service  on  overhead  trolley  lines  should  also  be  pro- 
vided with  lightning  arresters  and  choke  coils  to  prevent  a  rush 
of  current  through  the  motors  and  control  in  case  the  car  is  struck 
by  lightning  or  a  heavy  surge  occurs  on  the  line. 

Resistors  for  railway  service  have  already  been  considered  in 
connection  with  the  control  of  railway  motors,  and  with  electric 
braking.  If  grid  resistors  of  the  ordinary  type  are  used,  it  is 
essential  to  have  them  placed  in  such  a  position  as  will  insure 
adequate  ventilation,  or  the  operating  temperature  may  become 
so  high  as  to  burn  out  and  destroy  the  grids. 

Collectors. — For  all  roads  operating  with  overhead  contact 
lines,  some  kind  of  collector  must  be  used  to  make  contact  with 


FIG.  117. — Ordinary  wheel  trolley. 

The  wheel  is  carried  in  a  harp,  as  shown.     Current  is  conducted  from  the  wheel  to  the  harp 
through  spring  brass  contact  pieces,  bearing  on  the  ends  of  the  wheel  axle. 

the  trolley  wire.  The  usual  form  for  low-tension  direct-current 
roads  is  the  common  wheel  trolley.  This  device  is  so  well  known 
that  very  little  description  is  necessary.  It  consists  of  a  swivel- 
ing  base,  to  which  is  hinged  a  steel  pole  bearing  at  the  upper  end 
a  grooved  wheel  of  copper  or  bronze,  as  shown  in  Fig.  117,  which 
runs  on  the  lower  side  of  the  contact  wire.  Although  this  seems 
the  obvious  method  of  collecting  current,  it  was  not  invented  for 
several  years  after  the  operation  of  electric  cars  had  become  prac- 
tical; and  when  finally  developed  was  the  subject  of  litigation 
for  a  long  time.  To  keep  the  wheel  in  contact  with  the  wire  a 
spring  is  provided  in  the  base.  For  low-speed  roads  the  pressure 
required  to  maintain  contact  is  small:  but  as  the  speed  is  increased 

15 


226 


THE  ELECTRIC  RAILWAY 


the  needed  pressure  becomes  rapidly  greater.  This  is  largely 
due  to  the  uneven  surface  of  the  wire,  caused  by  the  sag  between 
suspension  points.  As  the  car  moves  along  the  track  toward  a 
point  of  support,  the  trolley  wheel  gradually  rises  until  the  hanger 
is  reached.  As  it  is  passed  a  rapid  change  in  the  alignment  of  the 
wire  takes  place,  and,  the  wheel's  upward  motion  being  suddenly 
arrested,  it  strikes  a  blow  on  the  wire.  The  force  of  the  blow 
depends  on  the  sag  in  the  wire,  the  speed  of  the  car,  and  the  stiff- 
ness of  the  spring  in  the  trolley  base.  If  the  spring  is  too  stiff, 
a  heavy  blow  is  struck;  while,  on  the  other  hand,  if  the  pressure 


10,000     1000 
8000  >,&00 

*o 

a 

6  000  ^  600 

1 
4000^400 

2000     ZOO 

\ 

\ 

\ 

x 

\ 

^r 

\^ 

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^ 

v 

^ 

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X 

10 


50 


60 


ZO        30         40 

Miles  cer  Hour. 
FIG.  118. — Effect  of  speed  on  current  collecting  capacity  of  wheel  trolleys. 

is  too  small,  the  wheel  may  leave  the  wire  entirely  at  times. 
This  latter  condition  is  especially  bad,  since  it  causes  a  succession 
of  arcs  which  pit  the  wire  and  the  wheel.  Pitting  the  wheel  has 
the  further  effect  of  roughening  the  surface  of  the  wire  at  other 
points. 

These  various  factors  cause  a  rapid  decrease  in  the  amount  of 
current  which  a  trolley  wheel  can  collect,  as  the  speed  is  raised. 
Although  the  capacity  of  the  contact  is  quite  large  at  low  speeds, 
the  current  which  can  be  successfully  delivered  to  the  car  is  much 
less  when  the  maximum  speeds  reached  in  ordinary  interurban 
service  are  attained.  The  relation  between  speed  and  current 
collecting  capacity  is  shown  in  Fig.  118. 

Coincident  with  the  reduction  in  current  capacity  as  the  speed 
is  increased,  there  is  a  marked  diminution  in  the  life  of  the  trolley 


CARS  AND  CAR  EQUIPMENT 


227 


wheels.     The  relation  between  the  life  of  wheels  and  the  maxi- 
mum speeds  attained  is  also  shown  in  Fig.  118. 

For  high-speed  roads,  other  forms  of  contact  have  been  tried. 
Of  the  ones  for  use  on  overhead  lines,  the  best  are  those  which 
replace  the  wheel  with  some  form  of  sliding  contact.  The  two 
principal  types  of  sliding  collector  are  the  bow  trolley  and  the 
pantograph.  Their  successful  operation  depends  to  a  large  ex- 


FIQ.  119. — Bow  trolley. 

This  design  is  better  suited  than  the  wheel  trolley  for  current  collection  at  high  speeds,  on 
account  of  i  ts  smaller  inertia.     It  is  widely  used  in  Europe. 

tent  on  making  a  structure  of  such  light  weight  and  small  inertia 
that  heavy  blows  will  not  be  delivered  to  the  wire  as  the  car  passes 
beneath.  At  the  same  time  it  has  become  customary  to  use  a 
form  of  construction  in  which  the  trolley  wire  is  held  more  nearly 
in  a  horizontal  plane.1 

The  bow  contact  is  made  in  two  entirely  different  forms.  The 
bow  trolley  proper,  Fig.  119,  replaces  the  trolley  pole  and  heavy 
wheel  with  a  light  framework  supporting  a  horizontal  contact 
piece  of  steel  or  aluminum,  which  is  held  against  the  wire  by 
means  of  a  spring,  or,  in  high-potential  equipments,  by  a  com- 
pressed air  cylinder.  With  the  latter  arrangement  it  is  unneces- 

1  See  Chapter  XII,  "Catenary  Suspension." 


228 


THE  ELECTRIC  RAILWAY 


FIG.   120. — Pantograph  trolley. 
This  type  is  in  use  for  current  collection  in  fast,  heavy  service,  such  as  on  trunk  lines. 


FIG.  121. — Over-running  third  rail  shoe. 

This  type  is  in  use  on  practically  all  the  elevated  roads  of  the  country.    It  is  only  suited 
to  the  unprotected  top-contact  rail. 


CARS  AND  CAR  EQUIPMENT 


229 


sary  for  the  operator  to  come  in  contact  with  the  live  portion 
of  the  circuit  in  any  way,  since  the  air  may  be  applied  by  remote 
control,  usually  being  worked  by  the  motorman  from  a  connection 
on  the  master  controller. 

The  pantograph  trolley,  Fig.  120,  consists  of  a  light  diamond- 
shaped  framework  carrying  at  its  top  the  contact  piece,  which  is 
similar  in  form  to  that  used  with  the  bow  trolley.  This  type 
is  almost  invariably  operated  by  compressed  air. 

On  third-rail  roads,  a  special  form  of  collector  must  be  used. 
Since  the  rail  is  carefully  aligned  with  the  track,  there  is  no  varia- 
tion in  level,  and  the  need  of  a  heavy  spring  to  insure  contact  is 
unnecessary.  For  over-running1  rails  a  very  simple  type  of  col- 
lector may  be  employed.  One  of  the  commonly  used  forms  is 
shown  in  Fig.  121.  It  consists  of  a  loosely  jointed  pantograph  of 


FIG.  122. — Slipper  shoe  for  under-running  third  rail. 

This  type  is  standard  for  bottom-contact  rails,  or  for  protected  top-contact  rails. 

small  dimensions,  carrying  at  the  bottom  a  contact  shoe  which  is 
held  on  the  rail  by  gravity  or  by  a  light  spring.  Connection  is 
made  to  the  car  wiring  by  a  flexible  cable.  When  the  under- 
running  third  rail  is  used,  a  different  form  of  shoe  is  employed, 
a  common  type  being  shown  in  Fig.  122.  This  shoe,  known  as 
the  " slipper  type,"  has  a  hinged  contact  piece  carried  from 
a  light  framework  attached  to  the  truck.  Its  action  is  obvious 
from  the  diagram.  This  shoe  is  also  excellent  for  over-running 
rails;  and  it  is  possible  to  arrange  it  so  that  it  may  be  used  inter- 
changeably for  either  top  or  bottom  contact. 

Car  Painting. — No  matter  what  the  materials  of  which  the  car 
is  built,  it  is  necessary  to  provide  some  sort  of  protective  coating, 
usually  paint  for  the  outside,  and  varnish  for  the  interior  over  the 
natural  wood.  The  proper  finishing  of  cars  is  a  subject  which  has 

1  See  Chapter  XII,  "Over-running  Third  Rail." 


230  THE  ELECTRIC  RAILWAY 

received  less  attention  than  it  merits,  for  on  it  depends  to  a  con- 
siderable extent  the  life  and  general  appearance  of  the  equipment, 
whether  the  material  be  wood  or  steel.  A  description  of  the 
methods  employed  is  out  of  place  in  this  book,  but  may  be  found 
by  reference  to  the  files  of  the  railway  periodicals. 

Miscellaneous  Details  of  Car  Equipment. — In  addition  to  the 
apparatus  already  considered,  there  are  many  minor  parts  of  the 
car  equipment  which  are  essential  to  successful  operation.  Seats, 
curtains,  ventilators,  door-operating  mechanism,  destination  and 
route  signs,  headlights,  markers,  and  a  number  of  other  parts  are 
all  necessary  to  make  the  equipment  complete.  While  a  detailed 
discussion  of  these  parts  of  the  car  is  unwarranted,  it  must  not  be 
forgotten  that  there  is  more  or  less  latitude  in  their  selection,  and 


FIG.  123. — Single  truck,  7-ft.  wheel  base. 

Trucks  of  this  and  similar  types  are  in  use  on  practically  all  of  the  single-truck  cars  in 
operation. 

that  considerable  care  should  be  taken  to  obtain  proper  and 
satisfactory  material. 

Trucks  and  Running  Gear. — The  operation  of  railway  vehicles 
makes  necessary  some  adequate  form  of  running  gear,  which  will 
carry  the  body  in  such  a  manner  as  to  prevent  objectionable 
shocks  and  vibration.  The  method  of  support  differs  widely,  the 
principal  variation  depending  on  whether  the  car  is  mounted  on  a 
single  rigid  framework,  or  has  two  swiveling  trucks. 

Single  Truck  Cars. — The  smaller  cars  for  city  service,  having 
bodies  not  more  than  about  20  ft.  long,  can  be  carried  with  sat- 
isfaction on  a  single  rigid-frame  truck.  The  construction  is  of 
the  simplest  character,  consisting  of  a  support  for  the  car  body  and 
pedestal  bearings  for  the  axles.  In  general,  a  rigid  mounting  of 
the  car  on  the  truck  is  undesirable,  so  that  some  form  of  spring  is 
interposed;  and  the  truck  proper  is  supported  on  the  journals  by 
helical  springs  over  the  pedestals  or  by  an  arrangement  of 
elliptical  or  semi-elliptical  springs.  The  single  trucks  produced  by 
different  manufacturers  vary  widely  in  their  details,  but  all  are 
quite  similar  in  general  appearance.  A  typical  single  truck  is 
shown  in  Fig.  123. 


CARS  AND  CAR  EQUIPMENT  231 

When  the  car  body  is  too  long,  difficulties  arise  in  the  design 
of  single  trucks.  In  order  to  operate  satisfactorily  on  city 
track,  where  the  curves  are  almost  invariably  of  short  radius, 
the  rigid  wheel  base  must  be  kept  to  a  minimum  length,  or  bind- 
ing of  the  flanges,  and  in  some  cases  more  serious  trouble,  will 
result.  If  the  wheel  base  is  short,  there  will  be  a  large  overhang 


FIG.  124.— Brill  radial  axle  truck. 

Note  the  action  of  the  hangers.     By  this  means  a  longer  wheel  base  can  be  used  on  a  gingle- 
truck  car  than  is  possible  with  the  design  shown  in  Fig.  123. 

at  the  ends  of  the  car,  giving  a  weak  structure,  and  causing  longi- 
tudinal oscillations  if  the  car  is  operated  at  high  speeds.  The 
ordinary  methods  of  spring  mounting  of  the  body  do  not  remove 
this  difficulty,  but  at  certain  speeds  may  aggravate  it.  The  sim- 
plest solution  is  to  use  two  swiveling  trucks  under  the  car;  but 
this  increases  the  expense,  and  may  appear  undesirable  if  the  car 
is  only  slightly  above  the  limiting  length.  Another  solution  which 


232 


THE  ELECTRIC  RAILWAY 


has  been  developed  is  to  carry  the  axles  on  hangers  which  may  be 
swung  at  an  angle  with  the  car  body  when  rounding  curves. 
With  proper  design,  the  hangers  can  provide  for  throwing 
the  axles  in  a  radial  direction  as  the  curve  is  reached,  restoring 
them  to  the  parallel  relation  after  getting  back  on  tangent  track. 
One  form  of  hanger  and  the  method  of  operation  are  shown  in 
Fig.  124. 

Swiveling  Trucks. — For  long  cars,  and  for  some  locomotive 
service,  it  is  necessary  to  use  two  swiveling  trucks  to  provide  for 
operation  around  curves.  The  trucks  are  independent  structures, 
and  are  each  connected  to  the  car  body  by  a  single  heavy  pin, 
or  "  king-bolt."  They  are  then  free  to  turn,  and  allow  the  wheels 
to  align  themselves  on  any  track.  This  construction  is  appli- 
cable to  cars  of  any  length.  In  order  to  prevent  dangerous  sway- 
ing of  the  car  body,  it  is  customary  to  provide  bearings  at  the 


FIG.  125. — Rigid  bolster  truck. 

Suitable  for  slow-speed  locomotive  service  only. 

sides  of  the  truck  to  limit  the  oscillation  of  the  car  at  high  speeds. 
These  may  be  either  flat  plates  or  ball  bearings.  For  the  latter 
it  is  claimed  that  the  friction  is  reduced  materially,  since  the 
trucks  are  more  free  to  align  themselves  with  the  track. 

The  principal  differences  in  trucks  are  in  the  methods  by  which 
the  car  body  is  hung.  The  simplest  way  is  to  support  the  bolster 
rigidly  from  the  truck  frame.  The  only  spring  possible  is  then 
that  over  the  pedestal.  Trucks  of  this  type,  as  shown  in  Fig. 
125,  are  only  suitable  for  slow-speed  locomotive  service,  the  cush- 
ioning being  insufficient  even  for  freight  cars. 

The  floating  bolster  construction,  shown  in  Fig.  126,  detaches 
the  bolster  from  the  rigid  connection  with  the  side  frames,  and 
supports  it  through  elliptical  springs  acting  in  a  vertical  plane 
transverse  to  the  direction  of  motion  of  the  truck,  the  bolster 
being  allowed  to  move  in  ways  provided  for  that  purpose.  While 


CARS  AND  CAR  EQUIPMENT 


233 


the  cushioning  is  better  than  with  the  rigid  bolster  construction, 
it  is  not  sufficient  for  high-speed  passenger  operation,  but  is 
chiefly  confined  to  freight-car  and  locomotive  service. 

A  further  development  is  the  swinging  bolster  truck.  In  this 
type  the  bolster  is  mounted  on  springs  traveling  in  a  guide,  as 
with  the  floating  bolster;  but  the  springs,  instead  of  resting  di- 
rectly on  the  side  frames,  are  carried  by  a  saddle  or  series  of  hang- 


FIG.  126. — Floating  bolster  (arch  bar)  truck. 

Suitable  for  freight  cars,  but  not  flexible  enough  for  passenger  cars. 

ers  which  allow  the  bolster  to  swing  in  a  transverse  direction. 
This  permits  the  car  body  to  roll  or  sway  on  curves  and  at  high 
speeds,  reducing  the  shock  to  a  minimum.  Trucks  of  this  kind 
are  standard  for  all  steam  and  electric  railway  passenger  cars, 
and  are  built  in  a  multitude  of  forms  for  every  class  of  service. 
A  widely  used  type  is  shown  in  Fig.  127. 


FIG.  127. — Swinging  bolster  truck. 

Suitable  for  high-speed  passenger  cars.     Trucks  of   this  general  type  are  made  in  a  wide 
range  of  forms. 

Maximum  Traction  Trucks. — It  has  been  shown  that  it  is 
desirable  to  use  a  minimum  number  of  motors  consistent  with 
obtaining  the  necessary  tractive  effort  for  car  operation.  For 
city  service  this  generally  calls  for  two  motors  per  car.  If  the  car 
body  is  too  long  for  a  single  truck,  ordinary  swiveling  types  can 
be  used ;  and  the  motors  may  either  be  mounted  both  on  one  truck, 
the  other  being  without  electrical  equipment,  or  one  may  be 


234 


THE  ELECTRIC  RAILWAY 


mounted  on  each.  When  the  cars  are  to  be  operated  in  either 
direction  the  latter  method  of  mounting  is  preferable,  since  the 
weight  transfer  between  the  trucks  is  then  equalized  for  both 
directions  of  motion.  In  cases  where  the  acceleration  demanded 
is  high,  the  use  of  two  motors  may  not  give  sufficient  adhesion, 
since  only  about  60  per  cent,  of  the  total  weight  is  carried  on  the 
motor-equipped  axles  (a  portion  of  the  motor  weight  is  carried 
directly,  accounting  for  the  increase  over  the  50  per  cent,  which 
might  be  expected).  The  weight  distribution  may  be  changed 
to  throw  a  greater  portion  on  the  driving  wheels  by  placing  the 
bolster  nearer  the  driving  axle.  In  this  way  the  available  ad- 
hesion may  be  increased  to  between  70  per  cent,  and  85  per  cent, 
of  the  total  car  weight.  Since  the  trailer  wheels  are  not  carrying 


FIG.  128. — Maximum  traction  truck. 

Used  for  city  cars,  in  order  to  employ  two-motor  equipments  with  high  accelerations. 

as  much  weight  as  the  others,  their  size  may  be  considerably  re- 
duced without  difficulty,  and  without  affecting  the  riding  qual- 
ities. In  this  form  the  " maximum  traction''  truck  has  been 
standardized,  and  is  used  on  a  number  of  roads.  One  style  is 
shown  in  Fig.  128.  A  feature  of  trucks  of  this  class  is  that  the 
small  wheels  may  be  allowed  to  extend  under  the  drop  platforms 
of  city  cars,  thus  increasing  the  total  wheel  base  beyond  what 
would  be  possible  with  standard  trucks.  This  tends  to  make 
the  car  easy  riding. 

All  maximum  traction  trucks  are  subject  to  one  objection. 
Since  a  large  portion  of  the  total  weight  has  been  transferred  to 
the  driving  wheels,  there  may  not  be  enough  weight  on  the  small 
ones  to  keep  them  on  the  rails  at  sharp  curves,  especially  at  high 
speeds.  For  this  reason  maximum  traction  trucks  are  considered 
unsafe  at  speeds  over  about  30  miles  per  hr.  If  higher-  speeds 
are  desired,  standard  trucks  should  be  used,  and  the  accelera- 
tion kept  down  to  a  point  where  there  will  be  no  danger  of 


CARS  AND  CAR  EQUIPMENT 


235 


exceeding  the  adhesion;  or,  if  the  high  accelerations  are  neces- 
sary, four-motor  equipments  should  be  used. 

Motor  Suspensions. — In  adapting  trucks  for  electric  opera- 
tion, it  is  essential  to  make  provision  for  mounting  the  motors  on 
them.  It  has  become  the  universal  practice  to  gear  the  motors 
directly  to  the  axles  without  intermediate  flexible  connections,  so 
that  it  is  necessary  to  maintain  the  gear  centers  at  a  constant  dis- 


FIG.  129. — Nose  suspension  (outside  hung  motor). 

This  method  of  support  makes  it  possible  to  carry  a  portion  of  the  motor  weight  on  springs. 
There  are  several  variations  from  this  arrangement. 

tance  to  ensure  their  correct  operation.  This  practically  means 
that  a  portion  of  the  motor  weight  must  be  carried  directly  on  the 
axle.  Generally,  bearings  are  provided  on  the  motor  case,  to 
give  the  necessary  support  for  the  machine  and  for  the  purpose  of 
aligning  the  gears.  The  remainder  of  the  motor  weight  may  be 
spring  borne  by  any  available  means. 


FIG.  130.  —  Gibbs  cradle  suspension. 

With  this  arrangement,   the  motors  mutually  support  each    other. 
equipments. 


Used    for   heavy 


The  simplest  and  oldest  arrangement  consists  in  using  a  lug  or 
nose  cast  directly  on  the  side  of  the  motor  case  opposite  the  axle 
bearings,  and  which  is  connected  to  the  side  frames  of  the  truck 
by  a  transverse  bar,  the  support  being  through  helical  springs. 
A  number  of  variations  in  this  form  of  construction  may  be  made. 
One  standard  type  of  mounting  is  shown  in  Fig.  129. 

Another  method  of  spring  support  consists  in  the  use  of  a  cradle 
in  which  the  two  motors  are  hung.  This  allows  them  to  mutually 


236  THE  ELECTRIC  RAILWAY 

carry  each  other  through  springs.  A  suspension  of  this  type  is 
shown  in  Fig.  130. 

The  motors  may  be  placed  either  between  the  axles  of  the  truck 
or  outside.  In  general,  it  is  better  to  place  them  inside,  since 
this  decreases  the  over  all  length  of  the  truck  and  gives  better 
weight  distribution  while  accelerating;  but  in  some  cases  the  wheel 
base  required  is  so  short  that  there  is  not  sufficient  room  for  the 
motors.  It  is  then  necessary  to  place  one  or  both  motors  out- 
side of  the  axles.  The  mounting  of  a  motor  in  this  way  is  shown 
in  Fig.  129.  This  construction  is  ordinarily  used  with  the  nose 
suspension,  and  is  adopted  only  for  light  trucks,  since  long,  heavy 
cars  are  not  well  suited  for  operation  around  curves  of  extremely 
short  radius. 

Motor  Gearing. — Ever  since  the  direct  form  of  drive  has  been 
used  for  railway  motors,  it  has  been  the  custom  to  use  high 
speeds  for  the  motor  armatures  with  considerably  lower  axle 
speeds.  This  reduces  the  weight  of  the  motor  for  a  given  output, 
and  permits  a  more  efficient  construction.  The  early  motors 
were  designed  for  extremely  high  speeds,  1000  to  1500  r.p.m. 
being  about  the  range  employed.  Since  the  axles  of  street  cars 
with  30-in.  wheels  rotate  at  100  to  200  r.p.m.,  it  follows  that  the 
speed  ratio  is  in  the  nature  of  10  : 1.  The  space  limitations  make 
the  greatest  practical  ratio  for  railway  service  with  a  pair  of  spur 
gears  about  3J/2  :1,  so  that  these  high  motor  speeds  call  for  a 
double  reduction.  After  a  few  years'  experience  with  this  ar- 
rangement, it  was  found  better  to  reduce  the  motor  speeds  some- 
what, so  that  a  single  pair  of  gears  could  be  used.  The  present 
street  railway  motors  have  armature  speeds  of  from  500  to  750 
r.p.m.,  making  a  single  reduction  entirely  practical. 

The  early  gears  were  of  cast  iron  or  malleable  iron,  and  the 
pinions  of  rawhide  or  soft  steel.  After  a  comparatively  short 
trial,  it  was  found  that  rawhide  could  not  stand  the  severe 
service  demanded,  and  steel  was  employed  exclusively.  The 
use  of  steel  pinions  with  cast-iron  gears  caused  the  most  of  the 
wear  to  fall  on  the  latter;  and  to  prevent  rapid  destruction  malle- 
able iron  was  substituted  for  cast  iron.  This  material  was  more 
economical,  but  it  was  soon  found  that  a  better  gear  could  be 
made  of  cast  steel,  with  greater  strength  and  longer  life  than  from 
malleable  iron. 

Although  cast  steel  has  given  considerable  satisfaction,  it 
has  not  proved  uniform  enough  in  quality  to  allow  of  its 


CARS  AND  CAR  EQUIPMENT  237 

being  worked  up  to  its  limit  of  strength.  More  recent  designs 
of  gears  have  been  made  of  forged  or  rolled  steel,  which  has 
at  once  greater  uniformity  of  composition  and  a  chance  for 
varying  the  ingredients  to  meet  the  needs  of  a  particular 
service.  Harder  steels  have  been  used;  but  it  has  been  found 
that  with  the  hard  steels  there  is  more  tendency  to  brittleness, 
which  may  cause  the  teeth  to  break  before  their  limit  of  wear 
is  reached.  To  obviate  this  difficulty  two  methods  have  been 
employed.  In  the  first  the  gears  have  been  made  of  a  low- 
carbon  steel  which  is  tough.  After  the  teeth  are  cut  the  gear 
is  treated  to  a  case-hardening  process,  giving  a  surface  which  is 
flinty  and  wear-resisting,  while  the  interior  remains  fibrous  and 
tough.  The  other  method  is  to  make  the  gears  of  a  metal 
which  will  allow  surface  tempering.  This  requires  a  steel  which 
is  somewhat  higher  in  carbon,  but  it  is  claimed  that  the  heat 
treatment  leaves  a  hard  wearing  surface  with  a  tough  core. 
Both  types  of  gear  are  in  common  use  now,  and  are  giving 
greatly  increased  life — in  many  cases  equaling  the  life  of  the 
axle  itself.  The  increased  life  with  the  improved  forms  of  gear- 
ing is  from  three  to  five  times  that  with  the  cast-steel  gear  and 
machinery-steel  pinion,  while  the  cost  is  from  one  and  one-half 
to  two  times  as  great.  In  figures,  the  life  has  been  increased 
from  about  100,000  miles  for  a  cast-steel  gear,  to  350,000  miles 
for  a  tempered  one  and  500,000  miles  when  case-hardened. 

While  the  wear  on  gears  is  severe,  that  on  pinions  is  still 
worse,  since  the  number  of  teeth  is  smaller.  Some  of  the  pinions 
are  made  of  case-hardened  steel,  and  others  of  heat-treated  steel. 
A  recent  development  is  the  use  of  tempered  tool  steel  for  pin- 
ions. It  must  not  be  overlooked,  however,  that  a  great  increase 
in  hardness  of  one  of  the  meshing  gears  above  that  of  the  other 
may  cause  wear  of  the  softer  metal. 

The  early  gears  were  cast  in  halves,  and  held  on  the  axle  with 
bolts.  This  construction  makes  it  easy  to  replace  damaged  gears, 
but  results  in  a  structural  weakness,  with  corresponding  liability 
to  breakage.  With  the  later  high-grade  gears,  lasting  about  as 
long  as  the  axles,  the  need  for  having  them  split  for  easy  removal 
has  disappeared,  so  that  it  is  preferable  to  make  them  solid  and 
press  them  permanently  on  the  axles. 

To  lengthen  the  life  of  the  gearing,  it  is  always  enclosed  in  a 
special  dust-proof  case.  The  cases  supplied  by  the  manu- 
facturers are  ordinarily  of  malleable  iron,  but  in  some  instances 


238  THE  ELECTRIC  RAILWAY 

they  are  made  of  pieces  of  sheet  steel  riveted  or  welded  together. 
Since  the  principal  function  of  the  case  is  to  protect  the  gears 
from  dirt  and  it  does  not  carry  any  other  parts,  its  mechanical 
strength  is  of  secondary  importance.  The  bottom  of  the  case 
comes  within  a  few  inches  of  the  top  of  the  rail;  and  if  there  is 
not  sufficient  strength  there,  it  may  be  crushed  or  broken  when 
obstructions  are  encountered  projecting  above  the  level  of  the 
rails. 

An  important  point  is  the  width  of  face  and  the  thickness  of 
tooth.  It  is  on  these  factors  that  the  size  of  gearing  is  deter- 
mined. Since  the  space  available  for  the  motor  is  limited  to  the 
distance  btween  the  wheel  hubs,  less  that  taken  by  the  gears,  it 
is  imperatve  that  the  width  of  face  be  kept  a  minimum.  Since 
the  only  other  dimension  which  is  capable  of  change  is  the  thick- 
ness of  tooth,  the  pitch  must  be  kept  a  maximum.  This  has  re- 
sulted in  diametral  pitches  of  2J^  to  3,  which  are  common  for 
motor  gearing.  Once  this  value  has  been  fixed,  the  total  number 
of  teeth  which  can  be  placed  on  the  gear  and  pinion  is  determined 
by  the  distance  between  centers.  When  a  motor  is  designed,  it  is 
necessary,  in  order  to  prevent  extra  cost  of  patterns  and  special 
machining,  to  keep  the  axle  centered  at  a  fixed  distance  from  the 
armature  shaft  for  all  motors  with  the  same  frame.  Since  the 
force  exerted  at  the  pitch  line  is  approximately  constant  for  all 
gear  ratios,  the  diametral  pitch  should  be  kept  uniform  for  all 
changes  in  speed  of  the  motor.  The  various  possibilities  for 
speed  reduction  lie  in  the  gears  whose  teeth  total  the  same.  For 
example,  if  a  certain  motor  is  designed  for  a  normal  gear  reduction 
of  20 : 59,  the  only  allowable  changes  from  this  are  such  as  will 
give  the  same  total  of  79  teeth  on  the  gear  and  the  pinion.  Pos- 
sible ratios  are  then  22:57;  21:58;  19:60,  and  so  on;  and  in  all 
these  combinations  the  strength  of  tooth  will  be  constant. 

The  limits  in  gear  reduction  are,  on  the  one  hand,  the  mini- 
mum diameter  of  pinion  or  the  maximum  size  of  gear  that  can  be 
used;  and  on  the  other,  the  dimensions  of  the  gear  case  which  can 
be  employed.  The  smallest  number  of  teeth  which  can  be  used 
on  a  pinion  without  undercutting  the  teeth  to  a  point  where  they 
are  materially  weakened  varies  with  the  form  of  tooth,  but  will 
generally  be  about  12  to  15.  This  gives  an  absolute  min- 
imum size  to  the  pinion,  and  a  limit  to  the  reduction  in  speed. 
The  gear,  on  the  other  hand,  must  not  be  so  large  that  there  will 
be  no  clearance  beneath  it,  or  there  will  be  danger  of  the  gear  case 


CARS  AND  CAR  EQUIPMENT  239 

striking  the  track.  This  limit  is  a  real  one,  for  the  ordinary 
minimum  clearance  beneath  the  gear  case  is  only  3  to  4  in. 
The  other  limit  is  seldom  reached,  for  the  maximum-speed 
equipments  are  not  nearly  so  much  in  demand,  and  a  very  low 
reduction  can  be  made  without  encroaching  on  the  clearance 
limits. 


CHAPTER  IX 
ELECTRIC  LOCOMOTIVES 

Development. — The  early  experimental  applications  of  electric 
power  to  traction  all  contemplated  the  use  of  locomotives.  This 
was  undoubtedly  due  largely  to  the  example  set  by  the  steam  loco- 
motive, which  was  at  that  time  the  accepted  motive  power  for  all 
classes  of  railways,  except  street-car  lines.  When  the  possibilities 
of  the  electric  motor  were  better  known,  it  was  seen  that  superior 
results  could  be  obtained  by  placing  the  entire  equipment  on  the 
cars,  thus  eliminating  the  unnecessary  dead  weight  incident  to 
locomotive  operation.  This  arrangement  has  become  standard 
for  all  street  cars,  and  for  rapid-transit  lines,  so  that  there  is  no 
field  for  the  electric  locomotive  in  these  classes  of  service. 

Advantages  of  Motor  Car  Trains. — For  such  roads  as  those 
mentioned  above,  there  are  several  advantages  to  the  use  of  motor 
cars,  which  cannot  be  obtained  when  locomotives  are  employed. 
Where  exceedingly  high  acceleration  is  a  prime  requisite,  the 
drawbar  pull  of  a  locomotive  would  be  so  great  as  to  make  it  a 
practical  impossibility.  For  instance,  the  express  trains  in  the 
New  York  subway,  consisting  of  seven  motor  cars  and  three  trail 
cars,  weigh  approximately  360  tons.  These  trains  are  accelerated 
at  a  rate  of  1.4  miles  per  hr.  per  sec.  up  to  a  speed  of  about  20  miles 
per  hr.,  the  maximum  running  speed  being  in  the  neighborhood 
of  40  miles  per  hr.  This  service  calls  for  a  tractive  effort  at  start- 
ing, on  straight  level  track,  of  approximately  53,000  lb.,  which 
must  be  maintained  up  to  about  20  miles  per  hr. ;  at  the  maximum 
speed  the  tractive  effort  is  roughly  4400  lb.  While  the  drawbar 
pull  at  starting  is  approximately  that  of  a  consolidation  locomo- 
tive of  standard  steam  railroad  design,  there  are  none  in  service 
which  can  maintain  it  up  to  the  high  speed  required. 

Another  advantage  of  the  motor-car  train  is  its  extreme  flex- 
ibility, when  operated  with  multiple-unit  control.  The  number 
of  cars  may  be  adjusted  to  suit  the  traffic,  since  each  can  be  made 
an  independent  unit.  The  motor  equipment  is  just  sufficient 

240 


ELECTRIC  LOCOMOTIVES  241 

to  give  the  desired  tractive  effort,  so  that  there  is  no  ques- 
tion of  underloading  or  overloading,  as  often  happens  with 
locomotives. 

Field  of  the  Electric  Locomotive. — When  cost  is  considered, 
motor  cars  do  not  compare  so  favorably  with  locomotives;  for 
the  large  number  of  comparatively  small  motors,  with  their 
complicated  wiring  and  control,  will  usually  cost  considerably 
more  than  when  the  same  power  is  concentrated  in  a  few  locomo- 
tive units.  The  flexibility  due  to  multiple-unit  control  can  be 
obtained  to  some  degree  with  the  latter,  for  these  can  be  built 
in  sizes  of,  say,  one-half  the  normal  capacity.  Such  units  can  be 
operated  singly  or  in  groups,  so  as  to  give  approximately  the  cor- 
rect power  for  any  train  in  use. 

The  example  cited  above  is  one  in  which  the  locomotive  could 
not  be  used  to  advantage.  This  is  generally  the  case  where  the 
service  is  severe,  and  the  acceleration  is  high.  But  where  the 
schedule  does  not  call  for  so  great  tractive  effort,  the  obvious 
advantage  of  the  locomotive  may  make  it  desirable  instead  of  the 
motor-car  train.  Such  operation  is  that  of  trunk  line  through 
trains  in  ordinary  passenger  service,  and,  in  general,  of  all  freight 
trains.  Although  the  use  of  individual  motor  cars  for  freight 
service  has  been  proposed,  there  is  no  doubt  but  that  any  elec- 
trification involving  the  haulage  of  large  amounts  of  freight  will 
call  for  locomotives,  operated  as  single  units  or  in  groups.  It  is 
in  such  service  that  the  electric  locomotive  has  its  field. 

As  compared  with  the  steam,  the  electric  locomotive  possesses 
the  great  advantage  of  capacity.  Since  the  boiler,  with  its  weight 
of  water,  and  the  tender,  with  a  considerable  load,  are  absent, 
the  entire  equipment  may  if  desired  be  used  for  adhesion.  The 
locomotive  being  essentially  a  pulling  machine,  any  weight  which 
is  not  used  for  adhesion  is  a  dead  loss;  and  this  weight  should 
be  kept  a  minimum. 

It  must  be  remembered  that  while  the  steam  locomotive  is  com- 
plete in  itself,  the  electric  engine  is  but  one  part  of  the  electric 
power  system.  While  the  output  of  the  former  is  limited  to  what 
it  can  develop,  the  latter  has  behind  it  a  source  of  power  which  is 
much  greater;  so  that  the  electric  locomotive  can  carry  overloads 
for  a  short  period  which  would  be  quite  beyond  the  capacity  of 
the  engine  and  boiler  of  the  ordinary  steam  locomotive. 

Due  to  the  inherent  characteristics  of  electric  motors,  the  lo- 
comotive is  better  adapted  to  haul  trains  at  high  speeds  when 

16 


242  THE  ELECTRIC  RAILWAY 

developing  maximum  tractive  effort,  than  is  the  steam  locomotive. 
For  this  reason  it  has  the  ability  to  pull  large  loads  at  consider- 
ably higher  speeds,  which  tends  to  increase  the  capacity  of  the 
track.  The  possibility  of  subdivision  makes  the  proper  selection 
of  units  easy  to  give  the  best  combination  for  any  class  of 
service. 

On  account  of  the  power-plant  apparatus  being  concentrated, 
the  stand-by  losses  incident  to  steam  operation  are  largely  elimi- 
nated. In  a  system  of  moderate  size  the  average  load  at  any 
period  of  the  day  can  be  made  fairly  constant,  so  that  the  boilers 
and  generating  equipment  are  loaded  near  their  maximum  capac- 
ity; and  the  losses  due  to  coal  consumption  while  locomotives  are 
ready  for  service,  but  not  actually  in  use,  are  very  small.  There 
is  no  need  for  long  periods  of  rest,  such  as  those  due  to  cleaning 
out  flues,  washing  boilers,  and  other  incidents  to  steam  operation; 
nor  is  there  i>he  waste  of  fuel  in  starting  fires  at  the  beginning,  and 
dumping  them  at  the  end  of  the  run.  These  characteristics 
materially  increase  the  amount  of  time  the  locomotive  can  be  in 
service,  so  that  the  total  number  of  units  required  is  less  than  for 
steam  traction. 

Wheel  Classification. — There  are  two  methods  of  notation  in 
use  for  representing  the  arrangement  of  wheels  on  locomotives. 
The  method  most  used  in  America  is  to  give  the  numbers  of  wheels, 
first  for  the  leading  truck,  then  for  the  drivers,  and  finally  for  the 
trailers.  A  locomotive  of  the  familiar  "  American  "  type  is  shown 
by  the  symbol  4-4-0,  there  being  a  four-wheeled  leading  truck, 
four  driving  wheels,  and  no  trailers.  In  the  European  classifica- 
tion system  the  numbers  of  axles  are  referred  to,  the  leading  and 
trailing  wheels  by  number,  and  the  driving  wheels  by  letter,  A 
being  equivalent  to  a  single  axle,  and  so  on.  Thus  the  American 
type  engine  would  be  represented  in  the  European  notation  as 
2-B-Q.  Since  this  method  of  designation  is  so  much  more  ex- 
pressive, differentiating  between  driving  and  idle  axles,  it  will  be 
used  in  this  chapter. 

The  table  on  page  243  shows  the  classification  of  standard 
American  steam  locomotives. 

While  the  wheel  arrangements  of  electric  locomotives  differ 
somewhat  from  those  given  for  steam  engines,  the  latter  are  use- 
ful for  reference  and  comparison. 


ELECTRIC  LOCOMOTIVES 

CLASSIFICATION  OF  STEAM  LOCOMOTIVES 


243 


Name 

Wheel 

arrangement 

Classification 

Per 
cent, 
weight 
on 
drivers 

Service 

American 

European 

Single 

Z  oo  Oo 

4-2-2 

2-A-l 

45 

Light       passenger 

driver 

(obsolete). 

American  .  :  Z  o  o  O  O 

4-4-0 

2-B-Q 

65 

Light  passenger. 

Columbia.   ZoOOo 

2-4-2 

l-B-l 

65 

Light       passenger 

(obsolete). 

Atlantic.  .  . 

Z  oo  O  Oo 

4-4-2 

2-5-1 

55 

High-speed      pas- 

senger. 

Forney1...  Z  COoo 

0-4-4 

0-J5-2 

50-65 

Suburban     (obso- 

lescent). 

Switcher1..  Z  OOO    . 

0-6-0      0-C-O 

100 

Switching         and 

helper. 

Mogul  .... 

ZoOOO 

2-6-0 

1-C-O 

86 

Light     freight 

(obsolescent). 

Ten-wheel.  Zoo  OOO 

4-6-0 

2-C-O 

75 

Passenger         and 

freight. 

Prairie  .... 

ZoOOOo 

2-6-2 

1-C-l 

75 

Heavy    passenger 

and  freight. 

Pacific.  .  .  . 

ZooOOOo 

4-6-2     '2-C-l 

60 

Fast,   heavy  pas- 

senger. 

Consolida-  ZoOOOO 

2-8-0     jl-D-0 

88 

Freight. 

tion. 

Mastodon.  Zoo  0000 

4-8-0 

2-D-O 

80 

Freight. 

Mikado..  .IZoOOOOo 

2-8-2 

1-D-l 

75 

Heavy  freight. 

Mountain  .ZooOOOOo 

4-8-2 

2-D-l 

70 

Very   heavy   pas- 

senger. 

Decapod..  ZoOOOO 

2-10-0 

l-E-0 

90 

Heavy  freight. 

Santa  Fe.  .,'  Z  o  O  O  OO  Oo 

2-10-2 

l-E-l 

80 

Heavy  freight. 

Mallet1.  .  .:  ZoOOO-OOOo 

2-6-6-2 

1-C  +  C-l 

85-100   Mountain  service. 

Electric  Locomotive  Types. — The  early  electric  locomotives 
were  nearly  all  direct  adaptations  of  motor  cars,  the  motor  capac- 
ity being  increased  so  that  one  or  more  trailers  could  be  hauled  by 
a  car,  usually  of  the  baggage  type.  This  practice  developed  until 
it  was  found  that  the  equipment  could  be  more  advantageously 
disposed  by  limiting  the  duty  of  the  motor  vehicle  to  pulling 
only.  This  led  to  considerable  variation  in  the  design  of  the 
superstructure;  but  the  fundamental  part,  the  trucks  and  running 
gear,  remained  the  same  as  in  ordinary  double-truck  cars.  Since 
the  object  is  to  develop  the  greatest  possible  tractive  effort  with 

1  The  wheel  arrangements  of  locomotives  under  these  same  names  vary 
somewhat.  Those  given  are  typical. 


244 


THE  ELECTRIC  RAILWAY 


the  available  weight,  such  locomotives  are  invariably  equipped 
with  four  motors.  The  general  arrangement  is  shown  in  Fig.  131. 
The  motors  are  of  the  ordinary  type,  with  single  reduction  gears. 
It  is  also  possible  to  use  gearless  motors  on  this  type  of  locomo- 

M aster  ^astss=(s^s^'n'f'o9raP^  Trolley 

Controller^    Main  Switch 

Blower 

,    Compressor 
Flexible  Blowe 
Connection* 


^Main  Reservoir 

FIG.  131. — B+B  geared  locomotive,  Southern  Pacific. 

Locomotives  of  this  general  type  are  in  use  on  many  interurban  railroads.     Note  the  com- 
pact arrangement  of  the  equipment. 

tive,  but  the  advantage  is  small  and  the  weight  and  cost  consider- 
ably greater  for  the  same  output.  It  is  mechanically  well  suited 
for  slow  operation;  but  when  run  at  high  speeds,  the  weight  sup- 
ported directly  on  the  axles  without  springs  is  so  great  as  to 
cause  pounding  of  the  track. 


FIG.  132. — 0-B-B-O  geared  locomotive,  Baltimore  and  Ohio. 

This  locomotive  is  well  suited  for  slow -speed,  heavy  freight  service. 

It  is  evident  that  the  entire  draw-bar  pull  of  the  swiveling-truck 
locomotive  must  be  transmitted  through  the  center  plates. 
This  renders  the  design  unsuitable  for  heavy  loads,  and  a  modi- 
fication has  been  made  by  articulating  the  trucks  together  and 
mounting  the  draft  gear  directly  on  them,  as  shown  in  Fig.  132. 


ELECTRIC  LOCOMOTIVES 


245 


The  cab  is  light  in  construction,  and  serves  principally  to  house 
the  control  apparatus. 

Locomotives  of  the  above  types  can  be  modified  for  high-speed 
operation  by  the  addition  of  leading  and  trailing  wheels,  which 
serve  to  guide  the  heavy  rigid  structure,  and  prevent  "nosing," 


!*_}_„_.] 3»fo=4---------~4 J 

H- - ,.-.~'..~,3*r--7-- -. I!. 


1 


FIG.  133. — 1-B  +  B-l  gearless  locomotive  New  York,  New  Haven  and 

Hartford. 

This  design  has  proved  excellent  for  high-speed,  heavy  passenger  trains  in  trunk-line 
service. 

especially  on  curves.  A  locomotive  of  this  type  is  shown  in  Fig. 
133.  This  represents  a  gearless  locomotive  built  for  the  New 
York,  New  Haven  and  Hartford  single-phase  line.  A  somewhat 
similar  design,  in  service  on  the  New  York  Central,  is  shown  in 
Fig  134.  In  this  design  a  four-wheeled  leading  and  a  similar 
trailing  truck  are  used. 


36'  0"- 

4f'o"    -- 

over  Couplers 


FIG.  134. — 2-D-2  gearless  locomotive,  New  York  Central. 

This  type  has  been  used  for  heavy  terminal  passenger  service.     The  dead  weight  on  the 
axles  is  rather  large  for  successful  operation  at  high  speeds. 

For  heavy  service,  especially  at  high  speed,  the  above  types 
have  not  proved  entirely  satisfactory.  Many  attempts  have  been 
made  to  improve  the  transmission  by  the  use  of  cranks  and  side 
rods.  These  designs  have  been  employed  to  a  considerable  ex- 
tent in  Europe,  and  to  a  much  smaller  degree  in  America.  The 


246 


THE  ELECTRIC  RAILWAY 


most  successful  one  in  the  United  States  is  that  of  the  Pennsyl- 
vania Railroad,  for  service  at  its  New  York  terminal.  This  en- 
gine is  shown  in  Fig.  135.  The  motors  are  spring-supported  on 
the  running  gear,  and  are  connected  to  jackshafts  which  in  turn 
drive  the  wheels  through  parallel  rods. 

When  the  motor  speed  is  too  high  for  direct  connection,  the 
motor  may  be  geared  to  a  jackshaft.     A  locomotive  of  this  class 


55 II ! 
64' II"- 
over  Couplers 

FIG.  135. — 2-B+B-2  gearless  locomotive,  Pennsylvania  Railroad. 

A  high-speed  passenger  locomotive,  with  crand  and  side  rod  drive.     Note  that  the  motors 
are  mounted  high  above  the  driving  wheels,  raising  the  center  of  gravity. 

is  shown  in  Fig.  136.  This  represents  the  latest  design  used  on 
the  Lotschberg  Railway  in  Switzerland.  Flexibility  is  accom- 
plished by  connecting  the  motors  to  the  driving  wheels  through 
"Scotch  yokes,"  which  permit  a  certain  amount  of  vertical  move- 
ment, while  there  is  no  horizontal  play  save  that  required  for 
the  bearings. 


FIG.  136. — 1-E-l  geared  locomotive,  Swiss  Federal  Railways. 

In  this  design  the  necessary  play  between  the  cranks  and  the  side-rods  is  obtained  by  the 
use  of  "Scotch  yokes." 

Application  of  Locomotive  Types. — For  slow-speed  service, 
such  as  freight  and  switching,  the  principal  requirement  is  to  get 
the  maximum  tractive  effort  from  the  available  weight.  For  this 
purpose  the  entire  mass  should  be  mounted  on  the  drivers,  leading 
to  the  swiveling  truck  or  articulated  types,  such  as  are  shown  in 
Fig.  131  and  Fig.  132.  These  designs  have  proved  entirely  sat- 
isfactory in  service  of  this  kind. 


ELECTRIC  LOCOMOTIVES  247 

For  fast  operation,  it  appears  almost  essential  to  place  a  por- 
tion of  the  total  weight  on  leading  trucks,  in  order  that  the  main 
mass  may  be  guided  along  the  track.  In  addition,  there  seems  to 
be  ground  for  believing  that  the  center  of  gravity  of  the  locomo- 
tive should  be  made  as  high  as  possible.  When  the  mass  is  low, 
there  is  little  cushioning  of  the  oscillations  as  the  locomotive 
moves  from  side  to  side  of  the  track,  due  to  irregularities  in  the 
alignment  of  the  rails.  The  parts  rigidly  mounted  on  the  axles 
are  especially  destructive  in  their  action.  The  result  is  excessive 
maintenance  costs;  and,  since  the  force  of  the  blow  depends  on 
the  kinetic  energy  of  the  moving  parts,  the  effect  increases  as  the 
square  of  the  speed.  On  the  contrary,  if  the  mass  of  the  locomo- 
tive is  high  above  the  track,  the  result  of  variations  in  the  align- 
ment is  to  cause  the  superstructure  to. sway,  while  the  wheels 
follow  the  small  irregularities  of  the  rails.  The  locomotive  is  not 
so  easy  riding;  but,  since  its  function  is  to  develop  tractive  effort, 
this  does  not  cause  any  operating  difficulty,  while  the  wear  on 
the  track  is  reduced.  For  this  reason,  designs  of  the  general  form 
shown  in  Figs.  135  and  136  have  been  developed  for  high-speed 
passenger  service. 

In  general,  to  secure  a  high  center  of  gravity,  it  is  necessary  to 
place  the  motors  on  the  superstructure  of  the  locomotive,  which 
causes  difficulty  in  making  a  mechanical  connection  with  the  driv- 
ing wheels.  This  inevitably  leads  to  a  design  embodying  cranks 
and  side  rods.  One  of  the  early  arguments  made  in  favor  of 
electric  locomotives  as  compared  with  steam  was  the  absence  of 
reciprocating  parts;  and  it  now  appears  that  it  may  be  impossible 
to  eliminate  them  from  electric  engines.  The  effect  of  the  rods  is, 
however,  not  so  destructive  in  the  latter  case,  for  the  motor  has 
a  rotary  motion,  giving  uniform  torque  at  all  points  in  the  revo- 
lution. In  order  to  transmit  the  motion  without  severe  twisting 
strains,  it  is  essential  that  cranks  be  placed  on  both  ends  of  the 
armature  shaft.  By  placing  them  90°  apart,  the  torque  will  be 
transmitted  uniformly  at  any  position;  for  the  action  is  compar- 
able to  the  addition  of  two  sine  waves  in  quadrature,  as  in  a  two- 
phase  electric  circuit.  The  sum  of  the  two  is  always  a  constant 
quantity.  On  account  of  this  uniformity  in  turning  effort,  the 
strains  on  the  track  are  not  so  severe  as  in  steam  practice,  and  the 
wear  on  the  reciprocating  parts  is  less. 

A  mechanical  difficulty  is  introduced  by  the  crank  and  side- 
rod  construction  which  does  not  exist  in  steam  locomotives.  Both 


248 


THE  ELECTRIC  RAILWAY 


cranks  are  attached  to  the  same  armature  shaft  and  driving 
wheels.  If  the  parts  are  not  in  perfect  alignment,  the  torsional 
strains  in  the  shafts  and  connecting  rods  will  be  great.  In  some 
cases  they  have  been  so  severe  as  to  shear  off  the  cranks  or  to 
break  the  shafts,  while  in  others  the  bearings  have  excessive 
wear.  The  obvious  remedy  is  extreme  accuracy  in  alignment  of 
the  cranks  and  bearings;  but  this  calls  for  careful  maintenance, 
which  cannot  always  be  obtained  in  the  ordinary  railroad  repair 
shop. 


700 


til  600 


I  500 


1 200 
& 


JOO 


.24        36         48         60         72 
Diameter  of  Wheel,  Inches. 
FIG.  137. — Revolutions  of  driving  wheels  per  mile. 

Geared  and  Gearless  Motors. — The  proper  speed  of  the  motor 
armature  and  of  the  driving  wheels  has  an  important  bearing  on 
the  design  of  the  mechanical  transmission  in  the  locomotive. 
The  electric  motor  is,  in  general,  essentially  a  high-speed  machine. 
If  it  is  to  be  directly  connected  to  the  drivers  the  wheel  diameter 
should  be  chosen  to  give  the  proper  armature  speed  for  econom- 
ical operation.  In  locomotives  for  fast  service,  this  is  not  very 
difficult.  The  relation  between  the  diameter  of  drivers  and  the 
revolutions  per  mile  is  shown  in  Fig.  137.  At  a  speed  of  60  miles 
per  hr.,  the  revolutions  per  mile  and  per  minute  will  be  the  same. 


ELECTRIC  LOCOMOTIVES  249 

With  44-in.  drivers,  as  are  used  on  the  New  York  Central  gearless 
locomotives,  the  armature  revolves  at  460  r.p.m.  at  this  train 
speed.  This  is  a  fair  value  for  motors  of  the  size  used.  Even 
with  72-in.  drivers,  as  on  the  Pennsylvania  locomotives,  the  speed 
is  280  r.p.m.,  which  is  not  excessively  low,  since  the  entire  loco- 
motive capacity  is  concentrated  in  two  machines.  But  if  similar 
gearless  locomotives  were  to  be  used  for  normal  speeds  of  20  to 
30  miles  per  hr.,  the  armature  speeds  would  be  so  low  as  to  be 
electrically  inefficient,  and  the  weight  would  be  excessive  for  the 
output. 

It  is  apparent  that  if  the  normal  speeds  are  to  be  low,  the  wheel 
diameter  must  be  reduced  for  a  gearless  locomotive.  If  the  mo- 
tors are  mounted  directly  on  the  axles,  this  will  probably  be  im- 
possible, since  the  armature  diameter  with  the  high-speed  motors 
is  so  large  that  there  is  little  excess  clearance  above  the  track. 
For  motors  driven  through  cranks,  the  wheel  size  may  be  reduced 
somewhat;  but  since  one  of  the  advantages  to  be  obtained  by 
crank  connection  is  the  raising  of  the  center  of  mass,  this  will  lead 
to  an  awkward  design.  The  difficulty  can  be  overcome  by  gear- 
ing the  motors,  for  then  the  motor  speed  may  be  chosen  to  give 
good  efficiency,  while  the  wheel  diameter  may  be  such  as  de- 
manded by  the  operating  characteristics.  There  are  many  rea- 
sons why  large  drivers  are  to  be  preferred.  They  give  more 
surface  of  contact  between  wheel  and  rail,  with  consequently 
greater  adhesion.  The  shocks  while  climbing  small  inequalities 
in  the  rails,  and  in  passing  bad  joints,  are  materially  less,  and  the 
wear  on  the  wheels  themselves  is  smaller.  A  gear  ratio  of  2  : 1 
makes  possible  the  use  of  a  motor  of,  say,  500  r.p.m.  with  40-in. 
drivers  at  a  normal  speed  of  30  miles  per  hr.  This  is  within  the 
limits  of  economy. 

The  application  of  geared  motors  for  low  speeds  may  be  made 
easily  in  the  swiveling  truck  designs;  or,  if  it  is  desired  to  concen- 
trate the  power  in  one  or  two  large  motors,  a  combination  of 
gears  and  side  rods  may  be  made,  as  in  Fig.  136.  By  this  means 
the  advantages  of  high  center  of  gravity  may  be  obtained.  While 
the  complication  is  somewhat  greater,  it  appears  to  be  justified, 
if  one  may  judge  by  recent  European  designs. 

Number  and  Coupling  of  Drivers. — An  examination  of  existing 
designs  of  locomotives,  both  electric  and  steam,  shows  a  wide 
range  in  the  number  of  drivers,  length  of  wheel  base,  and  methods 
of  coupling  wheels  together.  The  primary  limitation  of  the  track 


250  THE  ELECTRIC  RAILWAY 

is  the  maximum  load  which  can  be  safely  imposed  by  a  single 
wheel.  The  best  American  practice,  with  first-class  roadbed  and 
track,  limits  the  load  per  axle  to  from  50,000  Ib.  to  57,000  Ib. 
These  values  are  extreme,  and  should  be  used  only  when  the  track 
construction  is  the  best.  This  limit  will  then  determine  at  once 
the  number  of  driving  wheels  necessary  to  give  the  desired  tract- 
ive effort,  if  the  adhesion  coefficient  is  known.  This  latter  is 
usually  assumed,  for  purposes  of  design,  at  22  per  cent,  to  25  per 
cent.  A  driving  axle  load  of  50,000  Ib.  will  then  give  a  maximum 
tractive  effort  of  12,500  Ib.;  so  that  the  weight  on  the  drivers  may 
be  determined. 

The  weight  to  be  carried  on  the  idle  axles  depends  largely  on 
the  maximum  speed,  character  of  the  roadbed,  and  method 
of  equalization.  An  inspection  of  the  table  on  p.  243  shows  the 
American  practice  for  steam  locomotives.  For  electric  service 
the  proportion  of  the  weight  on  drivers  may  be  somewhat  greater, 
since  there  is  no  necessity  for  trailing  wheels,  which  have  been 
introduced  in  steam  locomotive  designs  to  allow  an  increase  in  the 
size  of  fire-box  for  large  capacities. 

The  number  of  driving  wheels  which  can  be  coupled  together  is 
limited  by  the  total  rigid  wheel  base  permitted.  This  is  deter- 
mined by  the  radius  of  the  maximum  curves  encountered,  since 
the  side  play  in  the  axle  bearings  is  restricted.  The  length  of 
rigid  wheel  base  may  be  increased  somewhat  for  slow-speed  serv- 
ice by  making  some  of  the  intermediate  drivers  without  flanges; 
but,  on  account  of  danger  of  derailment  at  high  speeds,  this  is  not 
to  be  commended  for  passenger  locomotives.  In  steam  practice, 
the  rigid  wheel  base  will  be  from  10  ft.  to  13  ft.  for  passenger 
locomotives,  and  from  10  ft.  to  17  ft.  for  freight  engines.  Longer 
rigid  wheel  bases  have  been  found  destructive,  both  to  the  track 
and  to  the  drivers.  In  steam  service  longer  wheel  bases  have  been 
made  possible  by  the  use  of  Mallet  articulated  locomotives,  in 
which  the  driving  wheels  are  assembled  in  two  separate  units,  the 
forward  engine  being  mounted  on  a  swiveling  truck.  In  electric 
locomotives,  the  result  may  be  attained  more  simply  by  the  use 
of  separate  units,  operated  together  by  multiple-unit  control. 

Evidence  has  been  introduced  to  show  that  the  tractive  effort 
which  can  be  developed  by  a  locomotive  will  be  increased  if  sev- 
eral driving  axles  are  coupled  together.1  This  is  to  be  expected, 
since  there  is  a  certain  amount  of  weight  transfer  between  the 

1  ELMER  A.  SPERRY,  Transactions  A.  I.  E.  E.,  Vol.  XXIX,  p.  1453. 


ELECTRIC  LOCOMOTIVES  251 

driving  axles  during  acceleration  and  retardation.  This  point 
has  already  been  considered  in  connection  with  train  braking. 
For  this  reason  it  would  seem  advisable,  if  several  axles  are 
mounted  on  a  rigid  frame,  to  couple  the  wheels  together,  by 
means  of  side  rods  or  by  gearing.  This  action  becomes  ap- 
parent only  while  accelerating  or  retarding,  so  that  for  certain 
classes  of  service  it  may  not  be  of  great  importance. 

Interchangeability  of  Locomotives. — In  many  cases  it  is  de- 
sirable to  be  able  to  use  the  same  locomotive  units  for  both  freight 
and  passenger  service.  When  this  can  be  done,  the  total  in- 
vestment in  motive  power  is  decreased,  and  the  necessary  repair 
work  Is  simplified.  The  factors  affecting  the  design,  as  it  has 
been  pointed  out  in  this  chapter,  make  it  somewhat  difficult  to 
build  a  "universal"  locomotive.  If  satisfactory  for  slow  speed, 
it  may  not  have  the  proper  riding  qualities  for  fast  service;  and 
if  properly  designed  for  high  speed,  it  will  be  excessive  in  weight 
and  cost  when  applied  to  slow-speed  work. 

When  geared  motors  are  used,  it  may  be  possible  to  approach 
the  desired  condition  by  using  different  gear  ratios  for  high-speed 
and  low-speed  service,  the  mechanical  design  being  otherwise  the 
same.  This  reduces  the  number  of  separate  parts,  but  does  not 
make  the  equipment  interchangeable.  A  compromise  may  be 
made  in  some  cases  by  operating  the  motors  at  different  potentials 
for  the  various  classes  of  service.  For  instance,  on  a  600-volt 
direct-current  locomotive,  the  motors  may  be  placed  in  parallel 
for  high-speed  passenger  operation,  and  in  series-parallel  for 
freight  service.  It  must  be  remembered  that  the  current  capac- 
ity of  the  motors  is  not  increased  by  this  procedure,  so  that 
when  running  in  series  each  motor  is  only  giving  about  one-half 
its  normal  rating.  On  roads  where  most  of  the  trains  are  in 
passenger  or  fast  freight  service,  this  method  may  give  satis- 
factory results.  The  fact  remains  that,  for  the  best  operating 
efficiency,  the  locomotives  should  be  designed  particularly  for 
the  service  they  are  to  be  used  on;  and  if  a  compromise  is 
necessary  it  must  be  effected  at  some  loss. 

Tractors. — A  recent  development  in  electric  locomotive  prac- 
tice is  to  increase  the  capacity  of  the  equipment  by  the  use  of 
auxiliary  tractors.  These,  as  used  on  one  American  railroad,1 
are  four-wheeled  motor  trucks,  which  are  operated  in  conjunc- 

1  Tractor  Trucks  and  Additional  Locomotives  for  Butte  2400- Volt  Railway, 
Electric  Railway  Journal,  Vol.  XLIII,  p.  1349,  June  13,  1914. 


252  THE  ELECTRIC  RAILWAY 

tion  with  the  locomotives.  There  is  no  control  equipment  on 
the  trucks,  but  the  motors  are  placed  in  series  with  those  on 
the  locomotive.  The  four  main  motors  are  wound  for  1200 
volts,  and  are  operated  two  in  series  in  normal  service.  When 
the  tractors  are  used,  the  additional  motors  are  connected  one  in 
series  in  each  circuit,  making  three  motors  in  series,  and  operat- 
ing at  approximately  two-thirds  normal  speed  in  parallel,  and 
one-third  speed  when  all  the  motors  are  placed  in  series.  Each 
tractor  weighs  approximately  one-half  as  much  as  a  standard 
locomotive,  so  that  the  drawbar  pull  is  increased  50  per  cent,  by 
its  addition.  Using  this  method  the  flexibility  of  the  equip- 
ment and  its  total  capacity  may  be  considerably  extended 
at  a  fairly  low  cost.  No  operating  data  have  been  published  to 
show  the  success  of  this  arrangement. 

Locomotive  Equipment. — The  equipment  required  for  electric 
locomotives  is,  in  general,  the  same  as  that  in  use  on  motor 
cars.  The  principal  difference  is  in  the  capacity  of  the  motors. 

The  location  of  the  motors  determines  largely  the  position  of 
the  auxiliary  apparatus  on  the  locomotive.  When  geared  or 
gearless  motors  are  used,  mounted  directly  on  the  axles,  there  is 
the  entire  space  above  the  main  frame  available  for  control 
equipment.  This  does  not  ordinarily  take  up  all  the  space,  so 
that  many  locomotives  of  this  class  are  designed  with  the  so- 
called  " steeple'7  cabs,  as  shown  in  Figs.  131,  132  and  134. 
When  the  motors  are  mounted  on  the  frame,  and  coupled  to 
the  driving  wheels  with  connecting  rods,  the  space  left  for  the 
apparatus  is  much  less,  and  the  cab  is  usually  built  over  the  en- 
tire locomotive  frame.  Such  designs  are  shown  in  Figs.  133, 
135  and  136. 

The  auxiliary  equipment  which  is  necessary  on  the  ordinary 
locomotive  consists  of  the  controller,  the  resistors  (if  used),  air 
compressor  and  governor,  transformer  (for  alternating-current 
locomotives),  and  the  miscellaneous  apparatus  needed  for  ease 
in  operation.  For  use  in  connection  with  standard  passenger 
cars,  a  boiler  for  supplying  steam  for  heating  is  a  necessity.  All 
of  this  equipment  is  comparatively  bulky;  and  in  the  latest 
designs  the  entire  cab  is  filled  with  it,  there  being  only  a  narrow 
passageway  on  each  side. 

Locomotive  Control. — Due  to  the  demand  for  independent 
units  which  may  be  operated  together  for  increased  output, 
practically  all  locomotives  are  provided  with  multiple-unit 


ELECTRIC  LOCOMOTIVES  253 

control.  On  account  of  the  large  amounts  of  power  handled, 
controllers  of  this  type  are  almost  essential  in  any  case,  since 
the  capacities  of  hand-operated  ones  are  not  by  any  means  ade- 
quate. It  is  interesting  to  note  that  in  a  recent  European  design, 
the  controller  is  of  the  drum  type;  but  this  is  an  exception  to  the 
usual  arrangement. 

For  heavy  locomotive  service,  the  variations  in  tractive 
effort  which  are  allowable  with  motor  cars  would  cause  de- 
structive jerking  during  acceleration.  For  this  reason  the 
number  of  steps  on  the  controller  is  invariably  greater.  Since 
the  acceleration  may  need  to  be  varied  to  suit  the  requirements  of 
each  particular  train,  automatic  control  is  seldom  used,  it  being 
considered  better  practice  to  place  the  operation  entirely  in 
command  of  the  motorman.  With  high-class  employees,  this 
method  gives  consistently  good  results. 

Choice  of  Locomotives. — It  may  appear,  at  first  sight,  that  the 
selection  of  the  proper  type  of  locomotive  for  a  particular  service 
is  subject  to  exact  rules.  Such  does  not  appear  to  be  the  case. 
The  locomotives  of  competing  manufacturers  for  almost  identical 
service  are  so  widely  at  variance  that  there  can  be  no  general 
agreement;  and  in  some  cases  the  same  manufacturer  has  used 
entirely  different  designs  for  similar  conditions. 

Electric  locomotives  are  still  subject  to  great  development; 
and  it  is  quite  possible  that  they  may  be  standardized.  It  must 
be  remembered  that  practically  all  of  them  in  service  have  been 
designed  within  the  past  ten  years,  while  the  steam  locomotives 
are  the  development  of  a  century's  study.  It  will  not  be  re- 
markable if  many  years  pass  before  the  electric  locomotive 
reaches  the  same  condition  of  standardization  as  its  steam 
competitor;  and  it  is  doubtful  if  this  is  desirable,  for  standardiza- 
tion on  a  large  scale  is  liable  to  mean  stagnation. 


CHAPTER  X 
SELF-PROPELLED  CARS 

Field  of  Self -Propelled  Cars. — Any  railroad,  whether  steam  or 
electric,  has  a  comparatively  high  cost  of  construction.  The 
gross  receipts  must  be  sufficient  to  cover  the  operating  expenses, 
and  leave  enough  margin  to  pay  interest  on  the  investment,  be- 
fore any  profit  can  be  realized.  A  certain  class  of  roads  exists 
in  which  operation  by  any  of  the  ordinary  methods,  such  as 
steam  locomotives,  or  electric  motors  fed  from  a  central  power 
station,  will  not  cover  the  expense.  The  steam  locomotive,  as 
has  been  shown,  is  at  its  best  only  in  large  units;  and,  if  several 
trains  per  day  are  to  be  run,  the  cost  of  operating  inefficient 
small  locomotives  may  be  prohibitive.  On  the  other  hand, 
the  electric  distributing  circuit  will  be  as  expensive,  in  many 
cases,  when  but  one  car  is  run  as  when  service  is  given  every 
hour.  The  interest  on  the  investment  and  maintenance  charges 
will  in  this  case  prohibit  successful  operation. 

It  is  for  this  class  of  roads  that  some  form  of  low-cost,  fairly 
efficient  service  must  be  given  if  a  railway  is  to  operate  at  all. 
Such  is  the  case  of  many  steam-road  branches  where,  in  order  to 
develop  traffic,  the  line  has  been  built  without  sufficient  knowl- 
edge of  local  conditions.  Another  instance  is  that  where  a  rail- 
road is  desired  to  develop  a  new  territory,  but  where  the  return 
may,  for  several  years,  be  inadequate  to  pay  expenses.  Such  a 
line  is  usually  a  feeder  to  a  large  steam  or  electric  railway  system. 
In  other  cases  the  cost  of  construction  may  be  excessive.  An 
example  of  this  is  the  cross-town  surface  lines  in  New  York  City, 
where  the  overhead  trolley  is  prohibited  by  law.  To  build 
underground  conduit  roads  of  the  type  used  on  the  main  through 
routes  would  cost  much  more  than  the  traffic  would  justify.  In 
each  of  these  cases  the  demand  is  for  a  cheaply  constructed 
track,  and  a  motive  power  which  will  give  satisfactory  service  at 
comparatively  low  cost.  It  is  for  this  reason  that  the  various 
self-propelled  cars  have  been  developed. 

254 


SELF-PROPELLED  CARS 


255 


Self-propelled  cars  can  also  be  used  during  hours  of  light  load, 
such  as  at  night.  With  infrequent  operation  of  this  sort  it  may 
prove  economical  to  shut  down  the  electric  power  plant  entirely, 
giving  the  required  service  with  self-propelled  cars.  In  this 
way  the  no-load  losses  incident  to  a  large  system  may  be 
eliminated,  while  at  the  same  time  an  opportunity  is  presented 
for  inspection  and  repair  to  the  power  plant  and  substation 
apparatus. 

At  the  present  time,  there  are  in  use  three  different  types  of 
self-propelled  cars,  which  cover  the  entire  range  of  service  needed. 
They  are  the  gasoline  type  with  mechanical  drive,  gasoline  with 
electric  drive,  and  the  storage  battery  car. 

Gasoline  Cars. — All  of  the  straight  gasoline  cars  in  the  United 
States  are  of  the  same  general  class,  being  the  product  of  one 
builder.  The  first  of  them  were  introduced  about  eleven  years 
ago  for  use  on  unprofitable  branch  lines  of  the  Union  Pacific 


oooooooooo 


CJ 


^-nnnnnnnhFir 


FIG.  138. — 55-ft.  gasoline  car,  mechanical  transmission. 

In  this  car  the  front  axle  is  the  driver,  the  engine  being  mounted  directly  above.     Note 
the  form  of  the  car  to  reduce  air  resistance. 

Railroad.  The  success  met  with  in  this  service  was  so  great  that 
cars  of  similar  type  have  been  built  for  a  number  of  roads  in 
various  parts  of  the  country. 

The  gasoline  driven  cars  are  of  somewhat  special  construction, 
as  shown  in  Fig.  138.  The  forward  end  is  reserved  for  the 
power  plant,  which  consists  of  a  200-hp.  internal  combustion 
engine,  directly  geared  to  the  front  axle  of  the  forward  truck. 
Speed  control  is  obtained  in  the  same  manner  as  in  the  gasoline 
automobile,  by  means  of  gears  and  a  free  engine  clutch.  Varia- 
tions in  the  charge  and  the  ignition  allow  still  further  .range  in  the 
control. 


256 


THE  ELECTRIC  RAILWAY 


The  cars  which  are  in  operation  are  from  55  ft.  to  70  ft.  in 
length,  and  are  somewhat  similar  to  those  for  standard  electric 
interurban  railways.  It  is  interesting  to  note  that  this  design 
of  car  is  the  only  one  in  regular  service  which  has  taken  advantage 
of  the  experimental  results  found  in  connection  with  air  resistance 
at  high  speeds.  The  front  is  wedge  shaped,  while  the  rear  end 
is  rounded.  The  roof  is  of  the  plain  arch  type,  and  all  of  the 
fittings,  such  as  windows  and  doors,  are  so  designed  as  to  give 
the  most  regular  contour  possible.  The  builders  claim  a  mater- 
ially reduced  train  resistance  due  to  the  construction. 

Gas-Electric  Cars. — There  are  two  distinct  types  of  gasoline- 
electric  cars  in  use  in  America,  both  of  which  embody  the  same 
general  features.  One  of  the  cars  of  the  General  Electric  Com- 
pany is  shown  in  Fig.  139,  and  a  similar  one,  manufactured  by  the 


*—  -v  L—  J  L__J   L_l  L_J   l__i  L—J  LJ  1—  J  L_J  L_J   1—  1  L  1      I— 

Kinnnnnnnnnnn? 

> 

tooooM 

l^^                      z*\_J 

00 

FIG.  139. — 70-ft.  General  Electric  gas— electric  car. 

The  gasoline  engine  drives  a  direct-current  generator  from  which  current  is  obtained  for 
operating  the  railway  motors. 

Drake  Railway  Automotrice  Company,  is  shown  in  Fig.  140. 
In  either  the  power  plant  consists  of  an  internal  combustion  en- 
gine, driving  a  direct-current  generator,  current  from  which  is 
used  to  operate  standard  600-volt  motors.  A  special  form  of 
series-parallel  controller  is  used,  which,  instead  of  inserting  re- 
sistance in  series  with  the  motors,  varies  the  field  strength  of  the 
generator.  By  this  method  the  control  is  made  more  efficient 
than  with  the  direct  mechanical  drive;  and,  since  the  motors  are 
able  to  deliver  maximum  tractive  effort  at  low  speeds  with  corre- 
spondingly reduced  power  input,  the  total  capacity  of  the  power 
plant  can  be  less  than  for  the  direct  drive.  This  allows  a  lighter 
gasoline  engine;  but  the  weight  of  the  entire  equipment  must 
necessarily  be  somewhat  heavier  for  the  electric  transmission, 
since  a  generator  and  a  set  of  motors  must  be  added. 


SELF-PROPELLED  CARS 


257 


In  practice,  the  operating  costs  for  the  three  types  of  gasoline 
cars  are  approximately  the  same,  varying  with  the  severity  of  the 
service  and  the  weight  of  the  equipment.  Either  type  is  fully 
capable  of  hauling  one  or  more  trailers  when  required,  so  that  the 
apparatus  is  exceedingly  flexible. 

Storage  Battery  Cars. — The  storage  battery  car  is  one  of  the 
oldest  developments  in  the  history  of  electric  traction,  being 
antedated  only  by  those  driven  by  primary  batteries.  In  the 
early  experiments,  batteries  of  the  types  obtainable  at  that  time 
were  tried  and  abandoned,  largely  on  account  of  the  great  weight 
of  the  equipment.  The  recent  improvements  in  storage  battery 
design  and  manufacture,  due  largely  to  the  advent  of  the  electric 
automobile,  have  made  it  possible  to  obtain  batteries  having 


:Ei 
,R 

-UUUUUUUU  L 

V                              Coach 

-nnnnnnnrt? 

UUL 

\>5moker 

Baggage 

Cab 

FIG.  140. — 70-ft.  Drake  "automotrice." 

This  car  is  similar  to  that  shown  in  Fig.  139,  but  is  of  somewhat  lighter  construction. 

much  greater  output  per  pound  of  weight,  with  increased  life. 
This  development  has  made  their  use  practical  for  propelling 
railway  cars  with  a  reasonable  efficiency. 

There  are  several  different  kinds  of  storage  battery  car  in  use 
at  the  present  time,  differing  principally  in  the  type  of  cells  em- 
ployed. Both  the  lead  and  the  Edison  nickel-iron  batteries  are 
used,  and  appear  to  be  giving  satisfaction.  One  type  of  car, 
following  largely  the  double-truck  stepless  design  of  the  New 
York  Railways,  and  in  use  on  the  same  road,  is  shown  in  Fig.  141. 

In  any  of  the  storage  battery  cars,  successful  operation  depends 
on  having  the  body  as  light  as  possible,  since  the  size  of  battery 
to  be  used  is  a  direct  function  of  the  weight  hauled.  Much  at- 
tention has  been  paid  to  this  feature,  and  exceedingly  low  weights 
per  seat  have  been  attained.  In  addition,  the  bearings  are  of 
the  anti-friction  types,  such  as  roller  or  ball  bearings.  Since  the 

17 


258 


THE  ELECTRIC  RAILWAY 


car  speeds  in  the  service  for  which  storage  battery  cars  are  best 
fitted  are  low,  the  train  resistance  consists  largely  of  journal  fric- 
tion; and  by  the  use  of  such  bearings  it  may  be  diminished  con- 
siderably. Some  of  the  makers  go  a  step  further  and  use  a  rigid 
axle  with  two  independent  wheels,  as  in  ordinary  wagons.  It  is 
claimed  that  this  reduces  the  friction  still  more,  especially  on 
curves.  No  extended  experiments  have  been  made  to  prove  this, 
and  it  is  possible  that  the  lower  friction  on  curves  may  be  offset 
by  increased  oscillatory  resistance. 

There  are  two  different  methods  of  operating  the  batteries. 
One  maker  advises  that  they  be  of  sufficient  capacity  to  give  a 


D 


U— J 


i— T 


FIG.  141. — Stepless  storage  battery  car. 

The  batteries  are  placed  under  the  seats.     The  motors  are  connected  independently  to 
the  wheels  by  chain  drive.     Friction  is  reduced  by  using  ball-  or  roller-bearings. 

whole  day's  run  without  recharging,  while  others  recommend  a 
smaller  battery,  with  a  full  charge  once  a  day,  and  short  ''boost- 
ing charges"  at  the  end  of  each  trip.  While  this  latter  method 
allows  the  use  of  a  battery  of  less  capacity,  it  does  not  give  such 
flexibility  in  service.  For  instance,  if  a  car  is  late  in  arriving  at 
the  charging  station,  it  will  not  receive  sufficient  charge,  and  the 
battery  may  be  exhausted  before  the  day  is  over,  or  else  the 
schedule  will  be  disarranged.  Trouble  has  resulted  in  a  number 
of  cases  from  this  cause,  and  has  made  it  an  open  question  as  to 
which  is  the  better  method  of  operation. 

The  motors  for  storage  battery  cars  are  much  smaller  than  those 
for  standard  electric  railway  service  with  equipment  of  equal 
weight.  This  is  largely  due  to  the  fact  that  the  acceleration 


SELF-PROPELLED  CARS  259 

and  the  maximum  speeds  are  low.  With  high  acceleration  the 
size  of  battery  required  becomes  so  great  as  to  render  its  use 
impractical. 

Storage  battery  cars  are  controlled  by  series-parallel  connec- 
tions of  the  batteries,  instead  of  the  motors,  although  by  com- 
bining the  two  methods  three  economical  running  speeds  may 
be  obtained.  Otherwise  the  arrangement  is  the  same  as  for 
standard  railway  equipment.  The  cars  may  easily  be  arranged 
for  multiple-unit  control;  and  in  some  cases  are  so  operated. 

Comparison  of  Self-Propelled  Cars. — It  is  evident  that  the 
various  types  of  self-propelled  cars  have  different  fields  of  service. 
Any  of  the  gasoline-driven  cars  are  capable  of  operation  over  any 
length  of  line,  and  are  limited  only  by  the  requirements  of  ob- 
taining fuel  and  having  sufficient  time  at  terminals  for  inspection 
and  repair.  Storage  battery  cars,  on  the  other  hand,  are  re- 
stricted in  action  by  the  amount  of  charge,  and  must  run  only 
between  points  where  electric  current  is  available.  There  must 
be  a  certain  time  of  inaction  during  charging,  whether  it  is  for 
a  single  long  period  per  day,  or  at  the  end  of  each  trip. 

The  gasoline  drive  may  be  suited  to  the  weight  hauled,  so  that 
there  is  no  limitation  to  the  size  of  car  which  can  be  equipped  with 
this  type  of  motive  power,  while  the  storage  battery  increases  in 
bulk  quite  rapidly  with  the  weight.  This  condition  is  inherent, 
and  cannot  be  overlooked  in  any  comparison. 

It  appears  that  the  gasoline  drive  is  best  suited  to  units  of 
comparatively  large  weight,  which  must  run  over  considerable 
distances,  and  at  fairly  high  speeds.  The  choice  between  the 
mechanical  and  the  electric  drives  depends  on  the  need  for  smooth 
acceleration,  and  efficient  operation  over  a  wide  range  of  speeds. 
The  running  expenses  are  nearly  the  same  for  both  types;  but 
the  first  cost  of  the  gas-electric  cars  is  somewhat  higher,  owing 
to  the  greater  amount  of  equipment.  They  are  also  slightly 
heavier  for  the  same  capacity.  The  wide  use  of  gas-electric  cars 
at  the  present  time  would  indicate  that  the  smoother  operation  is 
of  sufficient  value  to  warrant  the  extra  cost  and  weight.  Storage 
battery  cars  are  better  for  local  service  where  traffic  is  sparse, 
or  where  conditions  are  such  as  to  prohibit  the  use  of  overhead 
trolleys. 

It  is  not  to  be  expected  that  the  use  of  independent  units 
will  ever  supersede  the  ordinary  electric  railway  with  a  central 
power  plant  for  general  service,  for  a  limit  to  the  field  of  the  self- 


260  THE  ELECTRIC  RAILWAY 

propelled  car  is  reached  with  a  comparatively  low  traffic  density. 
This  can  be  determined  by  calculating  the  fixed  charges  and  run- 
ning expenses  of  the  two  methods.  On  comparison  it  will  be 
seen  that  the  operating  cost  of  any  form  of  self-propelled  car  is 
higher  than  that  for  standard  electric  equipment;  and  the  first 
cost  is  also  greater.  As  the  number  of  cars  in  use  increases,  the 
fixed  charges  on  the  power  plant  and  distribution  system  become 
proportionally  less ;  and  when  the  total  cost  becomes  equal  in  the 
two  cases,  the  advantage  of  the  independent  units  disappears. 
Actual  comparisons  show  the  field  of  this  class  of  vehicle  to  be 
limited  to  that  stated  at  the  beginning  of  the  chapter.  For  these 
special  forms  of  service  the  self-propelled  car  furnishes  a  valuable 
auxiliary  to  a  large  railway  system,  and  may  increase  the  earnings 
or  decrease  the  expense  by  a  considerable  amount. 

Gasoline  and  Special  Locomotives. — The  arguments  in  favor 
of  self-propelled  cars  do  not  apply  with  equal  force  to  locomotives, 
since  the  steam  locomotive  is  quite  satisfactory  for  nearly  all 
classes  of  service.  The  success  of  the  internal  combustion  motor 
has  led  engineers  to  believe  that  there  is  a  field  for  engines  of  this 
class,  and  several  designs  have  been  made.  At  present  a  few 
locomotives  with  internal  combustion  motors  are  in  service. 
A  road  having  a  small  amount  of  freight  business,  and  operated 
either  by  the  electric  system  or  by  self-propelled  cars,  may  have 
need  of  such  a  unit. 

The  mechanical  and  the  electric  drive  have  both  been  applied 
to  internal  combustion  locomotives.  One  type  of  the  latter,  in 
conjunction  with  the  Diesel  crude  oil  engine,  has  been  used  in 
Europe  for  some  time. 

In  connection  with  the  electrification  of  the  railroads  entering 
Chicago,  a  proposition  was  made  several  years  ago  to  use  storage 
battery  locomotives.  While  there  is  no  question  but  that  such 
equipment  is  a  possibility,  it  is  extremely  doubtful  whether  it 
could  show  sufficient  economy  in  operation  to  justify  itself.  Un- 
doubtedly the  total  running  cost  would  be  much  greater  than 
for  any  standard  form  of  electric  system  working  on  a  distributing 
circuit  from  a  central  power  plant. 


CHAPTER  XI 
ELECTRIC  RAILWAY  TRACK 

Track  Construction. — Although  the  requirements  of  all  rail- 
way track  are  essentially  the  same,  there  are  two  distinct  types 
of  construction  used,  depending  on  whether  the  railroad  is  laid 
on  private  right-of-way  or  in  paved  streets.  A  large  portion  of 
all  interurban  roads  are  built  on  private  property;  and  in  all 
such  cases  the  ordinary  construction  adopted  by  steam  roads 
can  be  used  to  advantage.  The  rails  are  of  standard  T-section, 
the  size  being  chosen  with  regard  to  the  amount  of  traffic  and 
weight  of  trains. 

In  track  construction  the  primary  consideration  is  good 
drainage.  There  should  be  a  well-settled  foundation  of  the 
natural  soil,  above  which  is  placed  a  layer  of  broken  stone  or 

?/.rj  (*- -4-0%-- >f   8p /b. /fair 

2  TiesS'xe'xS' 


FIG.  142. — Standard  interurban  track  construction. 

gravel  ballast,  from  8  to  12  in.  in  thickness.  On  this  are  placed 
the  cross-ties,  and  the  space  between  them  filled  with  the  ballast, 
which  should  be  well  tamped  beneath  the  ties  to  secure  them 
firmly  in  place.  With  this  construction,  the  porous  stone  ballast 
will  allow  surface  water  to  drain  off  readily,  and  so  keep  the 
foundation  dry.  It  is  necessary  to  provide  ditches  along  the 
side  of  the  roadbed,  at  a  level  below  the  bottom  of  the  ballast, 
in  order  to  drain  off  the  water  which  has  collected  on  the  track. 
In  this  way  the  entire  structure  will  be  more  permanent  and 
will  require  less  maintenance  than  where  the  roadbed  has  been 
poorly  built.  A  typical  form  of  railway  roadbed  is  shown  in 
Fig.  142. 

The  ties  in  use  are  generally  of  hard  wood,  such  as  cedar, 
oak  or  chestnut.     At  the  present  time  it  is  somewhat  difficult 

261 


262 


THE  ELECTRIC  RAILWAY 


to  secure  a  good  grade  of  such  materials;  and  the  practice  of 
using  soft  wood  ties,  such  as  pine  and  hemlock,  but  impregnated 
with  some  preservative  compound,  has  spread  rapidly.  The 
chemicals  in  general  use  are  creosote  and  zinc  chloride.  These 
are  applied  in  liquid  form,  the  ties  being  treated  either  in  the 
open  air  or  in  vacuum  tanks.  While  the  latter  process  is  more 
expensive,  it  gives  a  more  uniform  application  of  the  preservative, 
and  causes  it  to  sink  much  deeper  into  the  fiber  of  the  wood. 
Treated  ties  are  considerably  more  expensive  than  untreated 

ones;  but  the  soft  wood, 
when  properly  impregnated, 
has  at  least  as  good  life  as 
the  natural  hard  wood,  and 
the  cost  is  no  greater.  When 
hard  wood  is  treated  in  the 
same  manner,  its  life  may 
also  be  proportionally  pro- 
longed at  a  comparatively  low 
cost.  Indeed,  it  has  been 
possible  to  prevent  decay  to 
such  an  extent  that  the  life 
of  the  tie  is  determined  by 
mechanical  wear  from  the 
chafing  of  the  rails,  and  the 
destruction  of  the  fibers  by 
driving  spikes. 

In  the  older  track  construc- 
tion the  rails  are  laid  directly  on  the  ties,  and  are  fastened  in 
place  by  common  spikes.  The  mechanical  wear  on  the  ties  in 
such  construction  is  severe,  and  even  untreated  ones  may  be 
rendered  unfit  for  further  service  before  they  have  decayed. 
With  the  use  of  preservatives,  and  the  consequent  increase  in 
life,  many  roads  have  adopted  the  practice  of  placing  tie  plates 
under  the  rails  to  take  the  wear.  Another  advance  is  in  the 
use  of  screw  spikes  instead  of  the  common  driving  spikes.  This 
further  increases  the  life  of  the  ties. 

Track  Rails. — The  rails  in  use  are  of  the  standard  sections 
adopted  by  the  American  Society  of  Civil  Engineers,  the  American 
Railway  Association,  or  the  American  Electric  Railway  Engineer- 
ing Association.  A  section  of  the  standard  100-lb.  rail  adopted 
by  the  latter  is  shown  in  Fig.  143.  The  weights  used  vary 


FIG.  143.— Standard  100-lb.  T-rail. 

This  is  the  standard  T-rail  adopted  by  the 
American  Electric  Railway  Association.  Other 
sizes  are  quite  similar  in  shape. 


ELECTRIC  RAILWAY  TRACK 


263 


from  about  60  Ib.  per  yd.  to  100  lb.,  the  majority  of  rails  being 
from  70  to  80  lb.  for  interurban  construction. 

The  chemical  composition  of  rails  has  a  marked  effect  on  their 
physical  properties,  and  on  the  results  which  may  be  obtained 
from  them  in  service.  Where  the  roadbed  construction  possesses 
sufficient  flexibility,  the  composition  may  be  such  that  the  metal 
is  tough,  but  fairly  soft.  For  use  in  paved  streets,  where  the  sub- 
base  of  the  track  is  rigid,  as  when  laid  with  concrete,  a  harder 
rail,  possessing  greater  resistance  to  wear,  is  desirable.  The 
hardness  depends  to  a  large  degree  on  the  content  of  carbon, 
although  a  number  of  different  elements,  such  as  manganese, 
titanium,  nickel,  chromium,  silicon,  etc.,  may  be  added  to  vary 
the  properties  of  the  steel.  In  general,  since  the  wheel  loads 
on  electric  railroads  are  much  less  than  for  steam  trunk  lines,  the 
composition  may  be  selected  to  give  greater  hardness,  even 
though  the  metal  may  be  more  brittle.  The  recommendations 
of  the  American  Electric  Railway  Engineering  Association  for 
rail  metal  are  as  follows:1 


Elements 

Per  cent. 

Class  A 

Class  B 

Carbon  

0  .  60  to  0  .  75 
0.60  to  0.90 
Not  over  0  .  20 
Not  over  0  .  04 

0.70  to  0.85 
0.60  to  0.90 
Not  over  0.20 
Not  over  0  .  04 

Manganese 

Silicon 

Phosphorus  

Rail  Joints. — The  connection  between  rails  is  of  vital  im- 
portance. Rail  joints  are  either  suspended  or  supported,  de- 
pending on  whether  the  joint  is  placed  between  two  adjacent 
ties  or  on  top  of  one  tie.  The  forms  in  common  use  are  numer- 
ous, and  both  methods  of  support  are  used.  The  connection 
between  rails  is  made  by  means  of  two  plates,  known  severally 
as  " joint  plates,"  " splice  bars,"  " angles"  or  "fish  plates." 
These  are  of  special  rolled  sections  and  are  placed  one  on  either 
side  of  the  rail  ends,  being  bolted  to  each  rail.  The  simpler 
forms,  such  as  shown  at  (a)  in  Fig.  144,  consist  of  a  pair  of  plates 
which  are  drawn  in  against  the  base  and  head  of  the  rail  by 
bolts.  This  form  of  joint  may  be  either  suspended  or  sup- 

1  Engineering  Manual,  American  Electric  Railway  Engineering  Associa- 
tion, Section  Wr  2c. 


264  THE  ELECTRIC  RAILWAY 

ported.  The  " continuous"  rail  joint  is  shown  in  Fig.  144  (6). 
In  this  the  plate  is  continued  down  beneath  the  base  of  the  rail, 
forming  a  chair.  A  number  of  joints  of  this  general  design  are 
in  use  both  on  steam  and  on  electric  roads. 

Track  Construction  on  Paved  Streets. — In  cities,  where  the 
streets  are  paved,  it  is  necessary  to  build  the  track  in  such  a 
manner  as  to  interfere  as  little  as  possible  with  the  surface  of 
the  paving.  The  standard  T-rail  construction  may  be  used,  the 
paving  being  laid  on  top  of  the  ties  so  as  to  bring  it  flush  with  the 
head  of  the  rails.  Since  it  is  necessary  to  allow  space  for  the 
wheel  flanges  on  the  inside  of  the  track,  special  paving  blocks 


FIG.  144. — Types  of  rail  joints. 

(a)   Common  fish-plate  joint.  (&)  Continuous  rail  joint. 

are  sometimes  used  to  give  the  necessary  groove.  While  this  is 
satisfactory  where  the  travel  is  not  very  heavy,  it  is  not  so  good 
on  streets  which  are  much  used  for  heavy  teaming.  The  height 
of  the  ordinary  T-rails  is  not  sufficient  to  use  standard  paving 
blocks  with  a  cushion  of  sand  deep  enough  to  give  good  wear. 
This  defect  may  be  remedied  to  some  extent  by  using  special 
rails  with  a  high  web,  and  having  the  head  and  base  the  same  as 
the  standard  T-section.  In  many  of  the  large  cities  provision 
is  made  that  the  street  railway  tracks  must  be  available  for  wagon 
traffic;  in  some  it  is  provided  by  law  that  a  rail  of  a  tram  sec- 
tion, such  as  that  shown  in  Fig.  145,  must  be  used.  In  others, 
where  such  regulations  are  not  in  effect,  the  railroads  have  some- 
times laid  rails  with  a  grooved  head,  as  in  Fig.  146.  This  pro- 
vides no  path  for  vehicles,  which  is  a  good  thing  from  the 
standpoint  of  the  railway.  When  the  tram  section  of  rail 
is  used,  it  makes  an  excellent  roadway  for  vehicles,  the  wheel 
treads  running  on  the  projecting  lips  of  the  rails.  The 
difficulty  in  its  use  is  that  if  the  lip  is  below  the  rail  head  a 


ELECTRIC  RAILWAY  TRACK 


265 


U s"  A 


I- s% 4 


FIG.  145. — Tram  section    FIG.  146. — Grooved  section 
girder  rail.  girder  rail. 

Both  of  these  sections  have  been  used  to  a  considerable  extent  for  street  railway  track,  but 
re  now  almost  entirely  superseded  by  rails  of  the  general  type  shown  in  Fig.  147. 


FIG.  147. — 9-in.  Girder  rail  and  joint  plates. 

Used  in  city  construction  on  paved  streets. 


266  THE  ELECTRIC  RAILWAY 

sufficient  distance  to  allow  the  use  of  a  standard  wheel  flange,  it 
is  hard  to  get  vehicles  out  of  the  path  of  cars,  thus  delaying 
traffic.  A  compromise  has  been  effected  by  the  use  of  the  grooved 
rail  in  such  a  form  that  the  lip  is  far  enough  below  the  head  to 
provide  a  runway  for  vehicles,  and  at  the  same  time  make  it 
easy  for  them  to  leave  the  tracks.  The  design  for  a  9-in.  girder 
rail  with  joint  plates,  as  standardized  by  the  American  Electric 
Railway  Engineering  Association,  is  shown  in  Fig.  147.  This 
or  similar  designs  have  been  adopted  in  many  of  the  large  cities 
of  the  country,  and  have  proved  satisfactory. 

Special  Forms  of  Rail  Joints. — While  the  various  forms  of 
mechanical  joints  made  by  splice  bars  and  joint  plates  are 
entirely  satisfactory  in  open  construction,  they  must  be  care- 
fully maintained  and  tightened  as  the  bolts  wear  loose.  This 
requires  constant  inspection.  It  is  evident  that  where  the  track 
is  laid  in  city  streets,  and  completely  surrounded  with  paving, 
such  care  is  impossible.  It  is  essential  that  the  joints  remain 
in  good  condition  with  no  inspection  whatever,  and  that  the 
repairs  be  very  few,  since  each  time  one  is  made  it  means  to  tear 
up  and  replace  the  paving  around  the  joint. 

A  method  which  has  been  used  in  many  cities  is  to  weld  the 
rail  ends  together,  thus  forming  a  continuous  structure.  This 
arrangement  cannot  be  used  in  open  track,  since  the  expansion 
and  contraction  will  tear  the  track  loose  from  the  ballast  with 
every  change  in  temperature;  but  in  city  streets  it  can  be  em- 
ployed to  advantage,  since  the  rails  can  be  anchored  firmly  by 
the  paving,  so  that  the  temperature  changes  can  only  place  the 
rails  in  tension  or  compression.  As  the  rails  are  usually  laid 
in  the  hottest  days  of  summer,  the  track  will  be  in  tension  for 
nearly  the  entire  year,  and  there  will  be  practically  no  tend- 
ency to  buckle.  It  is  evident  that  this  construction  cannot  be 
used  to  advantage  on  curves. 

Cast  Welded  Joints. — There  are  three  methods  of  track  weld- 
ing which  are  in  general  use.  The  oldest  is  the  cast  weld.  In  this 
construction,  shown  in  Fig.  148,  the  rail  ends  are  joined  by  a  mass 
of  cast  iron  surrounding  them.  The  iron  is  melted  at  a  high 
temperature  and  poured  into  iron  moulds  around  the  rail  ends. 
This  chills  the  outside  surface  of  the  cast  metal,  so  that  the  in- 
terior has  its  temperature  raised  to  a  welding  heat,  and  an  actual 
weld  is  made  with  the  steel  of  the  rails.  This  form  of  joint  is 
quite  satisfactory,  the  principal  objection  being  that  extreme  cold 


ELECTRIC  RAILWAY  TRACK 


207 


weather  may  strain  the  cast  metal  beyond  its  tensile  limit  and 
crack  the  weld.     From  one  to  two  per  cent,  fail  in  this  manner. 

Thermit  Weld. — Another  method  of  rail  welding  is  by  the  use  of 
"Thermit."  This  is  a  patented  mixture  consisting  of  metallic 
aluminum  and  iron  oxide  in  proper  proportions,  with  other 
materials  added  to  obtain  a  metal  of  the  required  composition. 
This  is  supplied  in  the  form  of  a  powder,  which,  when  ignited, 
undergoes  a  chemical  reaction,  the  aluminum  combining  with  the 
oxygen  to  produce  alumina  and  metallic  iron  at  a  high  tempera- 
ture. The  powder  is  placed  in  crucibles  directly  above  the  rail 
joints,  which  have  been  previously  heated  by  some  external  means. 
The  mixture  is  ignited,  and  when  the  reaction  is  complete  the 
molten  iron  is  tapped  into  moulds  around  the  rail  ends.  The  weld 


FIG.  148.— Cast  weld. 


FIG.  149. — Thermit  weld. 


produced  is  not  unlike  the  cast  weld;  but  the  metal  is  of  a  different 
character,  being  of  the  composition  of  wrought  iron  or  steel, 
depending  on  the  ingredients  of  the  mixture  employed.  The 
temperature  of  the  molten  metal  is  much  higher,  so  that  a  more 
perfect  weld  is  obtained,  and  the  amount  of  iron  required  is 
considerably  less  than  for  the  ordinary  cast  weld.  The  appear- 
ance of  a  thermit  weld  is  shown  in  Fig.  149. 

Electric  Welding. — The  third  way  of  welding  is  with  the  aid  of 
the  electric  current.  There  are  two  distinct  methods  which  may 
be  used.  In  the  first,  which  has  the  widest  application,  joint 
plates  are  welded  to  the  sides  of  the  rail  ends  by  the  incandescent 
or  resistance  process.  This  consists  in  taking  current  from  the 
contact  line,  converting  it  to  alternating  current  by  a  rotary 
converter  or  motor-generator  set,  and  changing  to  a  low  potential 
through  a  stationary  transformer,  whose  secondary  winding  con- 
sists of  a  single  turn  of  heavy  bar  and  terminates  in  jaws  which 
are  placed  against  the  parts  to  be  welded.  The  diagram  of  con- 


268 


THE  ELECTRIC  RAILWAY 


nections  is  shown  in  Fig.  150.  The  resistance  in  the  secondary 
circuit  is  practically  all  concentrated  at  the  junction  between  the 
rail  and  the  joint  plate;  so  that  a  considerable  amount  of  heat 
is  generated  there,  and  the  temperature  is  raised  to  the  welding 
point.  By  applying  a  suitable  pressure  to  the  jaws,  an  actual 
union  of  the  metals  is  obtained.  The  entire  rail  section  is  not 
welded;  but  two  or  three  places  on  the  end  of  each  rail  suffice 
to  make  a  more  permanent  connection  than  is  possible  with  any 
of  the  usual  forms  of  mechanical  joints. 

D.C.  Trolley 


m- 

I    U  U  Primary 

f       I  /^^4~X  X~<H~^OvVim^ 


0000000 


Transformer 


Jo'irrr 
Plates 


Single  Turn 
•''Secondary 


'"Yielding  Jaws 


FIG.   150. — Diagram  of  connections  for  electric  welding  outfit. 
For  welding  rail  joints.     A  similar  set,  except  of  smaller  capacity,  is  used  for    welding 
bonds. 

Within  the  last  few  years  another  system  of  welding  has  been 
developed,  using  the  arc  method.  In  this  the  rail  is  made  one 
terminal  of  the  electric  circuit,  and  a  rod  of  carbon  the  other. 
The  heat  generated  when  an  arc  is  struck  between  the  carbon 
electrode  and  the  rail  is  sufficient  to  raise  the  metal  to  a  welding 
temperature,  and  even  to  melt  it.  By  this  means  plates  may  be 
welded  to  the  rails,  thus  forming  permanent  joints. 

Of  the  four  methods  of  welding,  the  " Thermit"  process  re- 
quires the  least  expensive  apparatus,  and  for  that  reason  is  ap- 
plicable to  roads  which  could  not  afford  the  more  costly  equip- 
ment. The  arc,  the  cast,  and  the  resistance  welds  require  more 
expensive  apparatus  in  the  order  named.  The  actual  cost  of 


ELECTRIC  RAILWAY  TRACK  269 

each  joint  depends  largely  on  the  number  to  be  made.  The  equip- 
ment for  electric  resistance  welding  is  so  expensive  that  it  is 
ordinarily  not  purchased  outright  by  the  railway  company, 
but  is  rented  from  firms  making  a  specialty  of  the  business.  The 
cost  of  making  joints  varies  from  about  $2.75  for  cast  welds  to 
$4.50  for  " Thermit"  and  $6.00  for  electric  welds  by  the  resistance 
process. 

Special  Work. — In  any  railroad,  it  is  not  sufficient  to  provide 
a  single  track  alone,  but  switches,  turnouts  and  crossings  must  be 
used,  their  number  and  complexity  varying  with  the  nature  of 
the  track.  Such  pieces  are  almost  invariably  built  by  manu- 
facturers who  make  a  specialty  of  this  business,  and  are  installed 
by  the  railroads  as  complete  units.  For  interurban  roads,  the 
number  of  different  parts  is  relatively  few,  and  they  may  be  kept 
in  stock  by  the  user.  But  for  railways  whose  tracks  are  built  in 
city  streets,  it  is  essential  that  the  construction  be  such  that  the 
parts  can  be  installed  with  a  minimum  of  difficulty,  and  that  they 
will  give  a  maximum  life,  since  the  replacement  is  a  difficult  piece 
of  work,  requiring  that  the  traffic  be  stopped  and  the  paving  re- 
moved. To  make  the  installation  as  simple  as  possible,  the  entire 
track  layout  for  a  switch  or  crossing  is  built  complete  by  the  manu- 
facturer, and  assembled  in  his  yards  prior  to  shipment.  When 
it  is  desired  to  replace  one  piece  of  special  work  by  another,  the 
parts  are  set  up  in  the  street  near  the  final  location,  while  the 
paving  is  removed  from  around  the  old  track.  At  a  period  of 
light  traffic,  usually  at  night,  the  old  track  is  removed  and  the  new 
slid  into  position,  it  having  been  fitted  previously  by  measurement 
so  that  a  minimum  of  adjustment  is  necessary. 

The  frogs,  switch  points  and  mates  are  the  parts  which  receive 
the  greatest  wear.  In  recent  years  it  has  been  found  possible  to 
increase  the  life  of  the  special  work  by  making  these  wearing 
parts  of  special  materials,  manganese  steel  being  used  very  largely 
for  the  purpose.  The  hard  inserts  may  be  cast  permanently  in 
position,  or  may  be  made  in  such  form  that  they  are  bolted  and 
wedged  in,  so  that  they  may  be  removed  and  replaced.  There  is 
always  some  danger  of  these  parts  becoming  loose  under  the  re- 
peated hammering  of  the  wheels;  and  at  the  present  time  this  is 
one  of  the  difficult  problems  of  track  maintenance.  It  is  beyond 
the  scope  of  this  book  to  take  up  the  details  of  special  work 
design;  but  much  information  on  the  subject  may  be  found  in  the 
current  engineering  periodicals. 


CHAPTER  XII 
THE  DISTRIBUTING  CIRCUIT 

The  Electric  Railway  Circuit. — The  problem  of  distributing 
electrical  energy  for  railway  service  by  means  of  a  constant  poten- 
tial system  is  theoretically  the  same  as  for  lighting  and  power, 
but  it  differs  therefrom  due  to  the  changing  location  of  the  load. 
It  is  this  characteristic  which  differentiates  railway  distribution 
most  radically  from  other  constant  potential  circuits. 

No  matter  whether  the  generating  system  is  connected  directly 
to  the  distributing  circuit,  or  through  a  transmission  system  and 
substations,  the  electrical  relations  in  the  contact  line  and  the 

Trolley  _ 


I  Generator 


Track 


Distance  from  Station 


FIG.  151. — Simple  distribution  circuit. 

The  generator  is  at  one  end  of  the  line,  feeding  directly  into  the  trolley  wire.     The  dia- 
gram at  the  right  shows  the  potential  at  any  point  when  the  car  is  at  the  far  end  of  the  track. 

auxiliary  conductors  are  essentially  the  same.  In  the  following 
discussion  it  is  understood  that  the  terms  " substation"  and 
" power  station'7  may  be  considered  synonymous  so  far  as  the  dis- 
tributing circuit  is  concerned,  the  difference  between  them  relat- 
ing to  other  parts  of  the  complete  power  system  which  will  be 
discussed  elsewhere. 

The  general  considerations  of  the  constant  potential  circuit 
necessitate  at  least  two  conductors  between  which  the  load  may 
be  connected.  Since  the  point  of  application  of  the  load  is  con- 
stantly changing,  it  is  essential  that  these  conductors  be  bare  to 
allow  the  moving  contacts  free  access  to  the  surface.  In  a  very 
large  proportion  of  all  electric  railways  the  track  rails  are  utilized 
for  one  side  of  the  circuit,  contact  being  made  through  the  wheels, 
while  a  wire  or  rail  is  used  for  the  other  conductor.  This  arrange- 

270 


THE  DISTRIBUTING  CIRCUIT 


271 


ment  causes  such  wide  differences  in  the  two  sides  of  the  circuit 
that  it  is  generally  simpler  to  consider  them  separately. 

The  simplest  railway  distribution  consists  of  that  for  a  single- 
track  road  fed  from  one  end,  as  shown  in  Fig.  151.  If  we  consider 
this  line  operating  a  single  car,  it  will  be  seen  that  at  the  substation 
the  full  potential  of  the  generating  machine  is  directly  available, 
since  the  drop  in  the  wiring  is  practically  negligible.  As  the  car 
goes  farther  from  the  station,  the  drop  in  potential  increases, 
being  greatest  at  the  distant  end  of  the  line.  If  a  constant  poten- 


1000    2000    3000  4000    5000     6000    7000     8000    3000 

Distance  from  Sfrot'ion.Feet 
FIG.  152. — Line  drop  for  simple  distributing  circuit  supplying  several  cars. 

The  circuit  is  the  same  as  that  shown  in  Fig.  151,  but  a  number  of  cars  are  being  operated, 
instead  of  one  as  in  the  former  case. 

tial  is  delivered,  the  drop  will  increase  directly  with  the  distance 
from  the  station,  its  value  being  determined  by  the  current  and  the 
resistance  of  the  conductor.  A  potential  diagram  is  shown  in  the 
figure.  If  the  station  potential  is  600  volts  and  the  car  is  at  the 
end  of  the  line,  drawing  such  current  as  to  give  a  line  drop  of  110 
volts,  the  average  pressure  supplied  to  the  car  is  evidently  490 
volts  if  the  current  demand  is  uniform.  Although  the  current 
will  vary  within  wide  limits,  its  average  value  will  follow  this  law. 
The  limiting  condition  will  then  be  to  determine  the  greatest 


272  THE  ELECTRIC  RAILWAY 

permissible  drop  with  the  maximum  current;  from  which,  by 
Ohm's  law,  the  size  of  the  conductor  required  may  be  found. 

The  single-car  line  is  seldom  met  with  in  practice.  Usually, 
a  number  of  cars  will  be  operated  on  the  road ;  and  if  they  are  all 
demanding  current  in  equal  amounts,  the  distribution  of  the 
potential  drop  will  be  quite  different  from  that  in  the  example  just 
given.  Consider  ten  cars  equally  spaced  along  a  line  10,000  ft. 
long.  If  each  is  demanding  a  current  of  100  amp.,  the  total  to  be 
delivered,  or  1000  amp.,  will  be  carried  from  the  station  to  the 
first  car,  900  amp.  from  that  point  to  the  second  car,  and  so  on, 
until  at  that  portion  of  the  line  beyond  the  ninth  car  the  current 
is  but  100  amp.  If  the  total  resistance  of  the  line  is  0.2  ohm, 
the  drop  in  potential  will  be  as  shown  in  Fig.  152,  being  greatest 
near  the  station  and  least  at  the  end  of  the  line. 

Had  the  entire  load  been  placed  at  the  end  of  the  line,  the 
total  drop  would  have  been 

0.2  X  1000  =  200  volts 
and  the  pressure  at  the  end  of  the  circuit 
600  -  200  =  400  volts 

as  shown  by  the  dotted  line  on  the  diagram.  It  may  also  be 
seen  that  with  the  entire  load  concentrated  at  a  point  5500  ft. 
from  the  station,  the  drop  would  be  the  same  as  in  the  actual 
distribution.  An  inspection  of  the  figure  shows  that  this  is  the 
average  distance  of  the  load  from  the  station. 

In  the  general  case,  if  the  total  load  is  made  up  of  a  number  of 
currents  7i,  72,  Is,  etc.,  located  at  distances  di,  d2,d3, etc., from  the 
station,  along  a  conductor  whose  resistance  per  unit  of  length 
is  r,  the  total  drop  e  at  the  farthest  point  is 

e  =  rdi(Ii  +  72  +  73  + +  /») 

+   r(dl    -    di)    (72    +   73    + +   In) 

+ +   r(dn    -    dn-l)In  (1) 

Equation  (1)  may  also  be  written  in  the  form 

e  =  r(dJi  +  dzh  +  dJ3  + +  dJn)  (2) 

It  is  often  desirable  to  get  the  "center  of  gravity"  of  the  load, 
which  is  usually  defined  as  the  point,  d,  at  which,  if  the  load 
were  concentrated,  the  drop  would  be  the  same  as  with  the 
actual  distribution,  or 

e  =  rd  S(7x  +  72  +  73  +  .  .  +  7n)  (3) 


THE  DISTRIBUTING  CIRCUIT  273 

The  last  term  of  this  expression  is  evidently  the  total  current, 
7,  delivered  to  the  system.  Using  this  value,  and  equating  (2) 
and  (3),  gives 


In  the  special  case  where  the  loads  are  all  of  equal  amount, 
and  are  uniformly  spaced,  this  becomes 

_  dji  +  2diJi  +  SdiJi  +  .    ... 

Ct      -  T 


+  3  +  .    ..  .    .    .+n) 


As  the  number  of  divisions  n  is  increased  indefinitely,  —  ~  — 

becomes  equal  to  one-half  the  total  number  of  divisions,  and  the 
second  member  of  equation  (5)  approaches  a  value  of  d  of  one- 
half  the  total  length  of  the  distribution.  This  is  a  special  case; 
but  on  roads  operating  a  considerable  number  of  cars  on  a 
uniform  headway  it  is  very  nearly  reached.  This  is  shown  by 
reference  to  Fig.  152.  If  the  load  were  uniformly  distributed  in 
this  case,  the  average  distance  would  be  5000  ft.  ;  with  the  given 
arrangement  it  is  5500  ft.  If  the  cars  each  moved  1000  ft. 
toward  the  station,  there  would  be  no  drop  for  the  first  one,  and 
the  average  distance  (center  of  gravity)  would  be  5000  ft. 

Use  of  Graphical  Time-Table.  —  The  application  of  this  principle 
depends  on  knowledge  of  the  actual  distribution  of  the  load; 
in  preliminary  work  it  cannot  be  known,  and  must  be  assumed. 
After  the  equipment  has  been  tentatively  decided  on,  the  speed- 
time  curves  for  the  various  runs  may  be  calculated,  and  from 
them  the  schedule  made  up.  In  practice  the  time-table  is 
laid  out  graphically,  as  in  Fig.  153,  using  time  as  abscissae  and 
distance  as  ordinates.  It  may  be  seen  at  once  that  this  con- 
sists of  a  set  of  distance-time  curves,  which  may  be  readily 
determined  from  the  speed-time  curves  by  integration.  Corre- 
sponding to  the  various  abscissae,  the  currents  being  taken 
by  the  cars  may  be  found,  and  the  total  gives  the  load  to  be 
distributed  over  the  section  in  question. 

Limiting  Drop.  —  The  determination  of  the  proper  value  for 
the  limiting  drop  is  the  most  difficult  part  of  the  problem. 

18 


274 


THE  ELECTRIC  RAILWAY 


Direct-current  series  motors  will  operate  with  some  degree  of 
satisfaction,  even  though  the  line  pressure  be  far  below  the  rated 
motor  potential,  but  will  run  at  lower  speed.  It  is  simply  a 
question  of  how  much  speed  reduction  will  be  tolerated  under 
the  worst  conditions  of  load  and  distribution.  With  alternat- 
ing-current induction  motors,  the  speed  is  not  changed  greatly 
with  reduced  potentials,  but  the  maximum  torque  and  the  per- 
formance of  the  machines  will  be  much  more  seriously  affected. 
Single-phase  commutator  motors  have  about  the  same  relations 


5  Art 


FIG.  153. — Graphical  time-table. 

Showing  the  location  of  all  cars  on  a  division  at  any  instant  of  time.     This  is  taken  from 
the  time-table  of  a  30-mile  interurban  railway  division. 

to  change  in  potential  as  direct-current  motors;  and,  since  they 
may  be  connected  to  different  taps  on  the  transformer,  the  net 
effect  will  be  still  less.  In  general,  the  permissible  drop  is 
usually  given  as  about  10  per  cent,  for  city  systems,  15  per 
cent,  for  suburban  systems  using  direct  current,  25  per  cent,  for 
direct-current  interurban  roads,  and  10  per  cent,  for  alternating- 
current  lines.  These  values  are  very  often  exceeded. 

If  the  motors  were  the  only  apparatus  using  the  trolley  current, 
the  drop  would  be  of  little  moment  except  as  it  changes  the  motor 
characteristics.  But  there  is  a  certain  amount  of  auxiliary  equip- 
ment, such  as  air  pumps,  lights  and  heaters,  which  must  also  re- 
ceive its  energy  from  the  line,  and  whose  performance  is 


THE  DISTRIBUTING  CIRCUIT  275 

more  seriously  affected.  Air  compressors  become  overloaded 
when  operated  on  reduced  pressure,  lamps  have  their  candle 
power  lowered  as  about  the  fourth  power  of  the  potential,  and 
heaters  their  heating  capacity  as  the  square  of  the  potential. 
For  these  reasons  it  is  desirable  to  have  fairly  good  regulation. 

In  certain  cases  the  section  of  conductor  calculated  to  give  the 
maximum  allowable  drop  will  be  found  wasteful  from  the  stand- 
point of  energy  loss.  The  most  economical  section  may  be  de- 
termined with  the  aid  of  Kelvin's  law,  which  is,  in  effect,  that  the 
minimum  annual  cost  of  the  line  is  reached  when  the  cost  of  the 
annual  power  loss  is  equal  to  the  value  of  the  interest  and  de- 
preciation on  the  investment.  The  application  of  this  law  to 
any  complicated  distribution  system,  such  as  that  for  a  city  rail- 
way, is  exceedingly  difficult;  but  for  a  simple  single-track 
interurban  line  it  admits  of  solution.  Unfortunately,  in  the  latter 
case,  the  most  efficient  section  of  conductor  is  almost  invariably 
smaller  than  that  warranted  by  the  maximum  permissible  drop. 

Methods  of  Feeding. — A  further  reference  to  Fig.  152  shows 
that  when  the  load  is  evenly  distributed  along  the  line,  the  drop 
is  not  by  any  means  uniform,  being  much  greater  near  the  station. 
It  would  seem  preferable  to  enlarge  the  conductor  section  near 
the  station,  even  if  the  resistance  at  the  far  end  of  the  line  had 
to  be  increased,  since  there  the  maximum  possible  current  is  quite 
small.  If  the  same  amount  of  conductor  material  is  properly 
arranged  with  reference  to  the  current  it  must  carry,  it  will  be 
of  a  maximum  section  at  the  station,  gradually  tapering  down  to 
a  small  size  at  the  extreme  end  of  the  line.  Practical  considera- 
tions make  the  complete  fulfilment  of  this  arrangement  out  of 
the  question ;  there  must  be  a  contact  line  of  fairly  large  section  to 
withstand  the  wear  incident  to  current  collection.  If  this  is  the 
only  conductor  which  need  be  installed  to  give  the  required 
section,  there  is  no  remedy  for  this  condition;  but  usually  a  sup- 
plementary conductor  must  be  added  to  limit  the  drop  to  the 
amount  determined  as  the  maximum  allowable. 

The  simplest  method  of  distribution  from  a  power  plant  or 
substation  is  that  shown  in  Fig.  151,  where  the  generator  is  con- 
nected directly  to  the  contact  line,  there  being  no  auxiliary 
conductor.  A  consideration  of  the  preceding  paragraphs  will 
show  that  this  is  uneconomical  of  copper,  since  the  section  should 
be  increased  where  the  drop  is  the  greatest.  It  has  been  inti- 
mated that  the  best  conductor  is  one  gradually  tapering  from  a 


276  THE  ELECTRIC  RAILWAY 

maximum  at  the  station  to  a  minimum  at  the  end  of  the  section ; 
but  such  an  arrangement  is  not  commercial  and  cannot  be  applied 
directly. 

The  most  usual  method  of  feeding,  especially  for  interurban 
roads,  is  to  place  a  supplementary  conductor  in  parallel  with  the 
contact  line,  connection  being  made  at  frequent  points,  as  shown 
in  Fig.  154.  This  arrangement  is  but  little  better  than  increasing 
the  section  of  the  contact  line,  although  the  supplementary  wire 

Feeder 


J L 


Jrolley 


Track 


FIG.  154. — Simple  feeder  system. 

This  is  little  more  than  the  equivalent  of  increasing  the  section  of  the  contact  line.     It  is 
widely  used  on  interurban  railways. 

can  be  protected  from  wear  and  therefore  have  a  minimum  rate 
of  depreciation.  In  interurban  systems,  taps  are  made  from  the 
feeder  at  from  every  500  ft.  to  every  2000  ft.,  depending  on  the 
character  of  the  road.  Taps  are  made  more  frequently  on  grades 
and  at  points  where  the  cars  must  be  accelerated. 

Another  method  of  feeding  is  to  separate  the  contact  line  into 
a  number  of  sections,  each  supplied  from  the  same  feeder,  as 

Feeder 


Trolley 


Truck 


FIG.  155. — Sectioned  conductor. 

This  arrangement  differs  from  that  shown  in  Fig.  154,  in  that  the  trolley  wire  is  cut  into 
sections  which  are  separated  by  insulators.  While  giving  protection  in  case  a  section  of 
the  circuit  is  damaged,  the  loss  is  considerably  greater. 

shown  in  Fig.  155.  This  arrangement  has  the  advantage  over 
the  system  shown  in  Fig.  154  that  contact  line  trouble  can  be 
localized  by  placing  fuses  or  circuit  breakers  in  the  feeder  taps. 
On  the  other  hand,  the  conductivity  of  the  contact  line  is  not  used 
to  its  fullest  extent,  so  that  a  larger  amount  of  copper  is  needed 
to  give  the  same  total  drop. 


THE  DISTRIBUTING  CIRCUIT 


277 


A  modification  of  the  first  method  is  shown  in  Fig.  156.  This 
differs  from  the  simple  system  in  that  the  feeders  are  run  sepa- 
rately, their  conductivity  being  chosen  to  equalize  the  drop  to 
some  extent.  By  careful  choice  of  the  size  of  conductors,  the 
drop  may  be  made  fairly  uniform  over  the  entire  section. 


Feeders 


{\  Generator 


Trolley 


Track 


FIG.  156. — Multiple  feeder  system. 

In  this  system  the  feeders  are  placed  in  parallel.     Their  size  is  so  proportioned  as  to 
equalize  the  drop  at  the  points  of  connection  with  the  trolley  wire. 

A  method  sometimes  used  is  shown  in  Fig.  157.  Here  the 
feeders  are  arranged  as  in  the  last  system,  but  the  contact  line 
is  sectioned  as  in  Fig.  155.  The  objection  is  the  amount  of  copper 
required  for  a  given  drop;  while  the  advantage  is  in  a  more  uni- 
form drop  over  the  entire  section  and  the  ability  to  localize 
troubles.  It  is  evident  that  in  this  arrangement  switches  to  the 


Feeders 


Iroltey 


Oenerafcr 


Track 


FIG.  157. — Sectional  feeder  system. 

This  is  similar  to  Fig.  156;  but  the  trolley  is  divided  into  sections  separated  by  insulators. 
They  may  be  connected  together  for  normal  operation  by  switches,  making  it  possible  to 
cut  out  of  circuit  a  damaged  portion  of  the  contact  line,  and  thus  maintain  partial  service. 

various  feeders  can  be  provided  on  the  switchboard,  and,  with 
automatic  circuit-breakers,  any  damaged  section  can  be  cut  out  of 
the  circuit  without  affecting  traffic  on  other  portions  of  the  line. 
Use  of  Boosters. — On  certain  long  lines,  the  ordinary  limita- 
tions of  maximum  drop  would  require  the  use  of  very  large  feed- 
ers. This  may  be  obviated  to  any  desired  degree  by  inserting 


278  THE  ELECTRIC  RAILWAY 

in  one  or  more  of  them  a  separate  series  generator,  known  as  a 
"  booster.'7  Such  an  arrangement  is  shown  in  Fig.  158.  Here  a 
simple  feeder  system  is  used  for  a  portion  of  the  section,  but 
in  order  to  keep  up  the  pressure  at  the  far  end,  a  booster  is  inserted 
in  the  longest  line. 

As  used  on  electric  railway  distribution  circuits,  the  booster 
is  a  series-wound  generator,  driven  by  an  engine  or  a  motor, 
and  having  its  field  and  armature  connected  directly  in  the 
feeder  circuit,  as  shown  in  Fig.  158.  The  number  of  turns  on 
the  field  winding  is  chosen  to  give  the  proper  e.m.f .  at  full  load 
to  compensate  for  the  drop  in  the  feeder,  or  if  desired,  to  over- 
compound  and  raise  the  pressure  with  the  load.  Such  an  ar- 
rangement is  automatic  in  action,  for  the  ampere  turns  on  the 
field  increase  directly  with  the  current,  and,  if  the  field  is  not 

Soosfer 


Feeder 


Trolley 
i  Generator 

Track 


FIG.  158. — Use  of  booster  for  feeding  system. 

saturated,  the  e.m.f.  generated  in  the  armature  is  in  proportion 
to  the  load.  The  compensation  for  line  drop  at  the  end  of  the 
feeder  may  therefore  be  taken  care  of  under  ah1  conditions  of 
operation,  without  the  necessity  of  constant  attention  by  the  sta- 
tion attendant.  Boosters  may  be  located  anywhere  on  the 
feeders  in  which  they  are  inserted;  but  are  commonly  placed  in 
the  substation,  since  there  they  are  under  the  supervision  of  the 
operator.  The  use  of  a  booster  does  not  reduce  the  drop.  The 
tendency  is  rather  to  augment  it;  but  by  increasing  the  e.m.f.  on 
the  feeder  the  pressure  at  the  end  of  the  line  is  kept  at  the  de- 
sired value.  At  the  present  time,  boosters  are  being  abandoned 
in  favor  of  better  location  of  substations. 

Requirements  of  the  Contact  Line. — We  have  seen  that  the 
distributing  circuit  for  an  electric  railway  differs  from  that  for 
any  other  application  of  electricity  principally  in  that  the  load 


THE  DISTRIBUTING  CIRCUIT  279 

is  never  fixed  in  location.  The  effect  of  this,  apart  from  all 
questions  of  capacity,  is  that  a  special  form  of  construction  must 
be  employed  to  permit  of  efficiently  connecting  the  load  with 
the  source  of  power.  This  movable  contact  must  have  as 
little  resistance  as  is  practicable,  and  it  must  be  reliable  under 
all  conditions  of  load  and  weather.  To  attain  these  desired 
criteria  has  been  the  aim  of  designers  of  electric  railway  apparatus 
from  the  beginning,  and  at  the  present  time  a  great  deal  has  been 
accomplished  toward  these  ends.  Contact  line  material  may 
be  made  as  reliable  as  conditions  warrant,  and  failures  of  first- 
class  construction  are  now  rare. 

Forms  of  Contact  Line. — There  are  in  general  use  at  the 
present  time  two  methods  of  distributing  electrical  energy  to 
the  moving  train:  the  overhead  trolley  and  the  third  rail.  In 
addition  to  these,  two  other  forms,  the  underground  conduit 
and  the  surface  contact  system,  have  been  used  to  a  small 
extent.  The  first  two  are  the  only  ones  which  have  any 
extended  application,  and  are  to  be  looked  to  for  future 
developments. 

The  Overhead  Trolley. — The  simplest  method  of  distribut- 
ing energy  to  a  moving  train  is  by  means  of  one  or  more  bare 
wires  strung  above  and  parallel  to  the  track.  If  a  direct-current 
or  single-phase  circuit  is  used,  the  track  may  be  made  the  return 
conductor.  By  this  means  the  contact  line  is  reduced  to  its 
simplest  terms:  a  single  wire,  arranged  to  make  connection 
with  the  moving  train  through  one  or  more  rolling  or  sliding 
contacts.  In  this  form  the  overhead  trolley  has  become  stand- 
ard on  a  very  large  proportion  of  all  the  electric  roads  of  the 
world. 

Methods  of  Suspending  Trolley  Wire. — Practically  all  over- 
head trolley  wires  are  arranged  to  have  the  moving  contact 
made  on  the  bottom  side  of  the  conductor.  To  make  this  scheme 
successful,  it  is  necessary  to  have  an  uninterrupted  surface  on 
which  the  car  contact  may  travel,  so  that  special  methods  of 
hanging  the  wire  have  been  devised. 

Any  flexible  wire  or  cable  freely  suspended  at  two  points, 
and  supporting  its  own  weight  alone,  will  assume  a  definite 
curve,  known  as  the  catenary.  The  equation  of  this  curve  is 
ordinarily  stated  as 

a     -         _ - 

y  =  oO  +  e  «)  (i) 


280 


THE  ELECTRIC  RAILWAY 


or  in  terms  of  hyperbolic  functions 


=  a  cosh  - 
a 


(2) 


where  x  and  y  are  the  coordinates  of  any  point  on  the  curve, 
referred  to  axes  as  shown  in  Fig.  159,  a  is  a  constant  depending 
on  the  length  of  span  and  the  sag  in  the  wire,  and  e  is  the  base  of 
the  natural  system  of  logarithms.  The  length  of  span  being 
L,  and  the  supports  at  the  same  level,  equation  (1)  becomes 

a  +  D  =     (e2a  +  e~2a)  (3) 


FIG.  159. — Equation  of  freely  suspended  wire. 
or,  from  equation  (2) 

a  +  D  =  a  cosh  ~~ 

The  corresponding  length  of  arc,  C,  is 

A         _A 

C  =  a  (e^a  —  e   2a) 


or 


•  i. 
2a  smh 


(4) 
(5) 
(6) 


Knowing  the  length  of  arc  and  the  deflection,  the  constant  a 
may  be  determined  by  the  following  equation: 


©'• 


D2 


2D 


(7) 


THE  DISTRIBUTING  CIRCUIT 


281 


If  only  the  length  of  span  and  the  deflection  are  known,  the 
constant  a  must  be  determined  by  means  of  successive  assump- 
tions and  approximations. 

The  stress  in  the  direction  of  the  curve  at  any  point,  S,  and  its 
horizontal  and  vertical  components,  H  and  F,  may  be  determined 
as  follows:  the  only  vertical  stress  must  of  necessity  be  that  of 
the  weight  of  one-half  the  total  wire.  If  the  weight  of  the  wire 

per  unit  length  be  W,  then 

CW 
F  =  ^  (8) 


and  from  the  parallelogram  of  forces, 

7 


and 


H  = 


V 


tan  6 


=  aW 


S  =  ~-a  =  (a  +  D)  W 
sin  0 


(9) 


(10) 


A  solution  of  the  above  equations  for  a  4-0  wire  and  a  span 
of  100  ft.,  with  different  values  of  a,  is  given  in  the  following 

table : 

STRESSES  IN  A  4-0  WIRE,  100-FT.  SPAN 


Constant,  feet,  a 

Sag,  feet,  D 

Length  arc, 
feet,  C 

Total  stress  in  Ib.  along 
direction  of  wire  (S) 

At  center  of 
span  =  H 

At  supports 

-  S 

25 

69.05 

181.34 

16.0 

60.24 

50 

27.15 

117.52 

32.0 

49.42 

100 

12.76 

104.22 

64.0 

72.22 

200 

6.28 

101.04 

128.1 

132.12 

400 

3.13 

100  .  26 

256.2 

258  .  20 

600 

2.08 

100.116 

384.3 

385.64 

1000 

1.25 

100.041 

640.5 

641.30 

2000 

0.625 

100.010 

1281.0 

1281.40 

4000 

0.311 

100  .  003 

2562.0 

2562.18 

8000 

0.156 

100.001 

5124.0 

5124.10 

Temperature  affects  the  curve  in  which  the  wire  hangs  by 
changing  its  length.  For  a  given  length  of  wire  at  any  tem- 
perature, that  at  another  temperature  may  be  found  by  the 
relation 

lt  =  10  [1  +  a  (t  -  t0)]  (11) 


282  THE  ELECTRIC  RAILWAY 

where  10  is  the  length  at  any  temperature  t0,  lt  that  at  another 
temperature  £,  and  a  the  linear  coefficient  of  expansion  of  the 
wire. 

In  the  case  of  a  wire  carrying  a  coating  of  ice  or  snow,  equations 
(4),  (5)  and  (6)  may  be  used  by  changing  the  value  of  W  to  in- 
clude the  weight  of  added  load  per  unit  of  length. 

The  above  equations  will  give  accurately  the  relations  existing 
in  any  suspended  wire  carrying  its  own  weight  alone,  as  in  the 
case  of  a  transmission  line  or  a  simple  trolley  wire.  It  may  be 
noted  that  to  keep  the  sag  down  to  values  permissible  for  contact 
lines  the  tension  must  be  considerable.  If  the  sags  are  too  small 
during  hot  weather,  they  may  reduce  to  such  a  point  when  the 
temperature  falls  as  to  strain  the  wire. 

As  an  example,  consider  a  4-0  hard-drawn  copper  trolley  wire 
strung  at  a  temperature  of  100°  F.  with  a  sag  of  2.08  ft.  The 
tension  at  the  supports,  as  given  by  the  table,  is  385.64  lb., 
which  is  but  a  moderate  load  on  a  wire  of  this  cross-section. 
If  the  thermometer  should  drop  to  23°  below  zero,  a  temperature 
not  infrequently  met  with  in  our  northern  states,  the  length  of 
the  wire,  determined  by  equation  (11),  is  100.001,  which  gives  a 
stress  of  5124.1  lb.  at  the  supports.  This  is  about  the  elastic 
limit  for  hard-drawn  copper,  and  there  is  danger  of  stretching  the 
wire.  If  there  were  any  considerable  ice  load  occurring  at  the 
same  time,  the  strain  might  reach  the  breaking  point. 

Catenary  Suspension. — An  attempt  to  obviate  this  condition, 
which  renders  high-speed  operation  difficult  in  hot  weather  on 
account  of  the  excessive  sag,  has  been  successfully  made  by  the 
use  of  the  so-called  "  catenary"  suspension  (Fig.  160).  This  con- 
sists in  supporting  the  contact  line  frequently  from  an  auxiliary 
or  messenger  wire,  usually  a  steel  cable  of  high  tensile  strength. 
The  trolley  wire  is  thus  divided  into  a  number  of  short  spans,  in 
which  the  sag  can  be  reduced  to  a  value  which  will  not  interfere 
with  high-speed  operation  of  the  trains. 

A  wire  or  flexible  cord,  uniformly  loaded  along  its  horizontal 
projection,  will  assume  the  curve  of  a  parabola.  This  curve 
differs  but  slightly  from  the  catenary  when  the  sag  is  compara- 
tively small,  so  that  the  combination  of  messenger  and  contact 
wire  may  be  considered  as  though  the  former  were  uniformly 
loaded  along  the  horizontal,  without  introducing  an  appreciable 
error.  The  approximate  deflection  of  a  wire,  calculated  by  this 
method,  is 


THE  DISTRIBUTING  CIRCUIT 
WL* 


D 


SH 


283 
(12) 


the  values  of  D,  W,  L  and  H  being  the  same  as  in  equations  (1) 
to  (10).     The  length  of  a  conductor  having  a  given  deflection  is 


C  =  L  (1  + 


(13) 


By  the  application  of  these  equations,  it  is  possible  to  determine 
the  deflection  of  the  messenger  cable  at  any  point  of  the  span, 
and  construct  a  set  of  hangers  of  such  lengths  that  the  contact 
wire  may  be  maintained  horizontal  at  all  points  of  support. 


FIG.  160. — Catenary  suspension. 

The  contact  wire  is  not  carried  directly,  but  is  suspended  from  a  series  of  hangers  attached 
to  a  messenger  wire  supported  on  the  brackets. 

The  use  of  the  catenary  suspension  makes  possible  a  material 
lengthening  of  the  span  without  increasing  the  sag  of  the  contact 
wire;  indeed,  with  a  properly  designed  set  of  hangers,  the  length 
of  span  may  be  determined  by  entirely  different  considera- 
tions than  the  sag.  An  important  point  to  note  is  that  varia- 
tions of  temperature  have  a  minimum  effect  on  the  level  of  the 
contact  line.  A  reduction  in  temperature  tends  to  decrease 
the  sag  of  the  messenger  wire,  but  at  the  same  time  it  shortens 
the  hangers  in  proportion  to  their  original  lengths.  The  long- 
est hangers  are  those  adjacent  to  the  supports,  in  which  location 
the  decrease  in  the  sag  is  least.  By  adjusting  the  tension  in  the 


284  THE  ELECTRIC  RAILWAY 

messenger  cable  for  an  average  point,  it  is  possible  to  reduce 
the  variations  in  height  of  the  trolley  wire  at  any  other  tem- 
perature to  a  minimum,  although  the  entire  contact  line  will 
rise  somewhat  in  cold  weather,  and  fall  in  hot  weather. 

A  wide  variation  exists  in  the  number  of  hangers  employed  with 
the  catenary  construction.  In  some  of  the  early  installations,  as 
many  as  fifteen  to  nineteen  were  used  for  a  single  span  of  from  150 
to  300  ft.  Experience  has  shown  that  such  a  number  of  hangers 
is  excessive,  and  that  a  material  reduction  can  be  made  with- 
out affecting  the  general  results  of  employing  this  type  of  sus- 
pension. But  in  a  few  instances,  the  desire  to  get  a  minimum 
cost  has  led  the  designers  to  cut  down  the  number  of  suspension 
points  to  where  the  advantage  of  the  construction  has  been 
largely  eliminated.  For  example,  a  few  installations  have  been 
made  with  three  suspension  points  for  a  150-ft.  pole  spacing. 
This  makes  the  effective  span  of  the  contact  wire  50  ft.,  or  about 
half  that  used  with  the  ordinary  bracket  construction,  and 
the  length  between  hangers  is  too  great  to  secure  a  level  wire. 
The  principal  advantage  remaining  with  this  minimum  number  of 
hangers  is  that  the  support  is  flexible,  instead  of  rigid  as  with 
plain  bracket  suspension.  In  modern  catenary  construction, 
the  number  of  hangers  for  a  150-ft.  span  is  from  five  to  nine,  de- 
pending on  the  speed  of  the  equipment  and  type  of  collector  used. 

Methods  of  Supporting  Wires. — There  are,  in  general,  two 
methods  of  supporting  the  contact  line:  the  span  wire  and 
the  side-  or  center-bracket.  The  former  construction,  shown 
in  Fig.  161,  consists  of  a  double  row  of  poles  carrying  steel  or 
iron  cables  placed  transversely  to  the  track.  The  contact  line 
is  suspended  from  insulators  attached  to  these  cross  wires.  The 
construction  is  equally  suited  to  single  or  double  track,  the  only 
difference  being  in  the  distance  between  the  poles  and  the  corre- 
sponding length  of  the  span.  This  arrangement  gives  a  fairly 
flexible  support  for  the  contact  wire,  and  minimizes  the  pound- 
ing at  the  insulators  due  to  the  passage  of  the  collectors  on  the 
moving  cars. 

Bracket  construction  consists  essentially  of  a  single  line  of 
poles,  on  each  of  which  is  placed  a  cross  arm  carrying  an  insulator. 
The  arrangement  may  be  adapted  equally  well  for  single  or  for 
double  track.  For  the  latter  the  poles  are  placed  on  the  center 
line,  between  the  tracks.  The  bracket  construction  is  some- 
what cheaper  than  the  span  wire,  but  has  not  the  same  flexibility. 


THE  DISTRIBUTING  CIRCUIT 


285 


FIG.  161. — Span  wire  construction. 

The  construction  is  useful  for  either  single  or  double  track,  using  the  arrangement  shown 
in  the  full  and  in  the  dotted  lines,  respectively. 


X  ~ 

FIG.  162. — Center  bracket  construction. 

This  construction  is  equally  well  suited  for  single  track,  omitting  the  portions  shown  in 
dotted  lines. 


286  THE  ELECTRIC  RAILWAY 

There  is  a  tendency  for  the  collectors  of  the  cars  or  locomotives 
passing  beneath  to  deliver  a  hammer  blow  at  each  point  of 
suspension.  This  type  is  shown  in  Fig.  162  for  a  double-track 
road.  For  a  single  track,  the  bracket  on  one  side  is  omitted, 
the  rest  of  the  construction  remaining  the  same. 

Either  the  bracket  or  the  span  wire  readily  lends  itself  to  the 
catenary  suspension.  The  messenger  cable  is  hung  from  the 
bracket  or  from  the  span  wire,  and  the  contact  line  is  attached 
to  the  messenger  by  hangers  of  suitable  lengths.  Since  enough 
flexibility  is  secured  by  the  catenary  suspension,  the  disad- 
vantages of  the  bracket  construction  disappear;  and  on  account 
of  its  lower  first  cost  it  is  the  type  usually  employed  for  single- 
track  or  double-track  roads.  If  a  greater  number  of  tracks 
are  equipped,  the  span  wire  is  cheaper.  In  some  cases  where 
there  are  many  tracks,  as  in  a  yard,  a  cross-catenary  suspension 
is  used  to  keep  the  span  wire  level,  thereby  insuring  that  all  of 
the  contact  lines  are  the  same  distance  from  the  ground. 

Use  of  Supporting  Bridges. — For  heavy  work,  as  in  railroad 
electrifications,  a  more  permanent  form  of  support  has  been 
used.  The  original  construction  of  the  New  York,  New  Haven 
and  Hartford  consists  of  light  bridges  built  of  structural  steel, 
placed  approximately  300  ft.  apart,  and  carrying  the  trolley 
wire  from  a  double  catenary.  The  latter  consists  of  two  mes- 
senger cables,  arranged  to  form  an  equilateral  triangle  with  the 
contact  wire,  which  is  at  the  bottom.  Each  point  of  support 
of  the  trolley  wire  is  hung  from  both  suspension  cables,  and 
these  are  kept  the  proper  distance  apart  by  a  spacer.  The 
wear  on  the  original  trolley  wire  was  so  great  that  it  was  decided 
to  install  an  auxiliary  contact  conductor  beneath  the  copper 
one.  This  new  contact  line  is  of  steel,  and  is  connected  to  the 
copper  wire  at  points  midway  between  the  main  hangers.  By 
this  means  an  extreme  flexibility  in  the  vertical  plane  is  ob- 
tained, combined  with  considerable  rigidity  in  the  horizontal 
direction. 

The  double  catenary  suspension  has  been  found  better  than  the 
requirements  of  the  heaviest  trunk-line  service  demand.  The 
later  construction  of  the  New  Haven,  and  that  of  other  main  lines, 
has  been  made  with  a  single  catenary,  light  steel  poles  or  bridges 
being  used  for  support. 

Size  of  Contact  Conductor. — The  proper  size  of  the  contact  line 
may  be  determined  from  electrical  relations;  but  it  is  important 


THE  DISTRIBUTING  CIRCUIT  287 

to  have  it  of  sufficient  section  to  withstand  the  mechanical 
strains  which  are  imposed  on  it.  For  interurban  construction, 
the  most  used  size  of  contact  conductor  for  overhead  trolley 
lines  is  4-0  wire,  while  for  city  construction  2-0  is  quite  often  used. 
The  odd  sizes  of  wire,  0  and  3-0,  are  but  rarely  employed.  The 
use  of  wire  for  the  contact  line  involves  some  method  of  support 
which  will  not  interfere  with  the  smooth  operation  of  the  collect- 
ing device.  When  the  ordinary  round  section  of  wire  is  employed, 
it  is  necessary  to  hold  the  wire  by  ears  partially  surrounding  it. 
This  causes  "hard  spots,"  sometimes  resulting  in  damage  to  the 
overhead  construction  after  long  periods  of  use.  Various  non- 
circular  sections  of  wire  have  been  used  from  time  to  time;  but  the 


FIG.  163. — Standard  4-0  grooved  trolley  wire. 

This  is  standard  with  the  American  Electric  Railway  Engineering  Association.     Other 
sizes  are  of  similar  section. 

only  one  which  has  met  with  wide  adoption  is  the  grooved  type, 
as  that  shown  in  Fig.  163,  which  represents  a  section  of  the 
standard  4-0  grooved  wire  adopted  by  the  American  Electric 
Railway  Engineering  Association.  The  cross-section  of  other 
sizes  is  similar  in  shape.  This  type  of  wire  is  held  by  ears  which 
grip  it  in  the  grooves,  and  therefore  offer  no  obstruction  to  the 
movement  of  the  collector.  It  is  used  extensively  in  interurban 
and  in  city  construction. 

The  Third  Rail. — In  cases  where  large  amounts  of  current  must 
be  collected,  especially  at  high  speeds,  the  overhead  trolley  has 


288  THE  ELECTRIC  RAILWAY 

not  been  found  entirely  satisfactory.  Part  of  this  is  due  to  the 
restricted  area  of  contact  between  the  moving  collector  and  the 
wire,  and  the  remainder  to  the  inequalities  of  the  surface  caused 
by  the  variation  in  height  of  the  wire.  For  such  roads  the  use  of 
the  so-called  "  third  rail "  gives  better  results.  This  is  essentially 
a  steel  conductor  supported  on  insulators  contiguous  to  and 
parallel  with  the  track.  In  most  cases  it  is  placed  at  one  side  of 
and  a  few  inches  above  the  running  rails.  Occasionally  it  is 
located  on  the  center  line  of  the  track,  and  still  more  infrequently 
is  suspended  above  the  track  in  a  position  similar  to  that  of  the 
ordinary  trolley  wire.  These  latter  dispositions  of  the  third  rail 
are  quite  rare,  and  are  adopted  to  meet  special  conditions.  In  the 
following  paragraphs  the  location  of  the  rail  at  one  side  of  the 
track  is  the  only  one  considered.  There  are  two  " types'7  of 
third  rail  in  use,  according  to  the  location  of  the  contact  surface. 
Over-Running  Third  Rail.— The  older  form  of  third  rail 
construction,  and  the  one  most  commonly  used,  is  that  in  which 

Contact  Kail 

....••• "Track  Rails  ••• "•••.. ..v 


FIG.  164. — Unprotected  over-running  third  rail. 

This  construction  is  used  on  all  the  elevated  roads;  the  exact  position  j>f  the  contact  rail 
varies  somewhat. 

the  contact  surface  is  the  top  of  the  rail.  In  this  type  of  con- 
struction, Fig.  164,  the  rail  is  mounted  on  insulators  of  porcelain, 
reconstructed  granite,  or  other  suitable  material.  An  ordinary 
rail  section  is  most  often  employed,  although  in  a  few  cases 
special  designs  have  been  used  to  reduce  the  cost  of  manufacture 
and  to  give  a  rail  more  readily  mounted. 

Many  persons  look  on  the  third  rail  as  a  source  of  danger,  due 
to  the  possibility  of  accidental  contact  from  persons  working  along 
the  track.  To  prevent  such  occurrence,  it  has  become  customary 
to  "protect"  the  rail  by  making  the  metal  inaccessible.  At  the 
same  time,  the  contact  surface  must  be  kept  free  for  the  passage 
of  the  collector.  It  is  quite  difficult  to  effectively  protect  the 
third  rail  where  the  top  contact  is  used.  A  number  of  devices, 
such  as  the  mounting  of  boards  parallel  to  the  rail,  at  one  side  and 
above  it,  have  been  tried  with  indifferent  success.  Forms  of 


THE  DISTRIBUTING  CIRCUIT 


289 


protection  are  shown  in  Fig.  165.  A  trouble  with  the  unpro- 
tected rail  is  that  it  is  liable  to  have  a  thin  coat  of  ice  form  over 
its  contact  surface  during  sleet  storms.  This  film,  although  some- 
times very  thin,  is  a  good  insulator,  and  occasionally  prevents 
train  movements  entirely.  Various  methods  have  been  tried 
to  combat  the  difficulty.  Some  roads  use  steel  scrapers  attached 
to  the  trucks,  passing  over  the  rail  surface  ahead  of  the  contact 
shoes.  Others  spray  the  rail  with  an  ice-resisting  liquid,  such  as 


FIG.  165. — Forms  of  protection  for  over-running  third  rail. 

These  are  used  to  prevent  accidental  contact  of  persons  walking  along  the  track  with  the 
live  conductor. 

salt  or  calcium  chloride  solution.     The  first  expedient  is  not 
entirely  successful,  and  the  second  may  affect  the  insulation. 

Under-Running  Third  Rail. — In  order  to  more  completely 
protect  the  third  rail,  and  at  the  same  time  to  lessen  trouble  from 
snow  and  sleet,  the  under-running  contact  has  come  into  use  in 
the  last  few  years.  The  rail  is  suspended  from  hangers,  as 
shown  in  Fig.  166,  with  insulation  at  the  supports.  It  is  a 
simple  matter  to  protect  against  ordinary  accidents  by  cover- 


FIG.  166. — Under-running  third-rail  construction. 

ing  the  top  surface  with  a  wooden  trough,  or  with  a  special 
clay  tile.  Sleet  does  not  form  so  easily  on  the  under  surface  of 
the  rail,  and  little  or  no  trouble  has  been  experienced  from  this 
source.  The  principal  objection  to  the  under-running  third 
rail  is  that  it  encroaches  more  on  the  clearance  limits  of  ordinary 
rolling  stock;  so  that,  unless  special  care  is  taken  to  eliminate 
cars  having  parts  outside  the  clearance  limits,  fouling  will  re- 
sult, with  consequent  interruption  of  service. 

19 


290 


THE  ELECTRIC  RAILWAY 


In  some  cases  rails  of  the  same  chemical  composition  as  the 
track  rails  are  employed;  but  frequently  they  are  made  of  a 
special  composition  selected  to  give  maximum  conductivity. 
The  principal  point  is  to  have  a  soft  steel,  with  a  minimum 
amount  of  impurity.  Such  a  composition  would  be  too  soft  for  a 
running  rail,  but  its  conductivity  can  be  increased  from  one-third 
to  one-half  above  that  of  the  rail  steel;  and  its  hardness  is  sufficient 
to  stand  the  wear  that  is  produced  by  the  rubbing  of  the  contact 


0-02. 


50 


60  70  80  90 

Weight,  Pounds  per  Yard 


100 


no 


FIG.  167. — Resistance  of  rails  with  bonds. 

shoes  on  its  surface.  The  resistance  of  rails,  complete  with 
bonds,  is  shown  in  Fig.  167. 

With  the  third  rail,  the  conductivity,  even  for  comparatively 
light  cross-sections,  is  so  great  that  little  additional  feeding 
capacity  is  needed,  except  on  very  heavy  systems. 

Underground  Conduit  Systems. — In  a  few  cities,  the  opposi- 
tion to  the  overhead  trolley  for  esthetic  reasons  has  been  so  great 
that  it  has  been  absolutely  prohibited.  In  the  United  States  the 
only  instances  are  New  York  and  Washington.  In  these  cities 
it  has  been  necessary  to  furnish  electric  street  railway  service 
without  the  use  of  overhead  construction.  The  third  rail,  as 


THE  DISTRIBUTING  CIRCUIT 


291 


ordinarily  used,  is  of  course  out  of  the  question  for  use  on  city 
streets.  Two  alternatives  remain :  to  place  the  conductors  under- 
ground, contact  being  made  through  a  slotted  conduit,  or  else 
by  a  system  of  surface  contact.  Both  have  been  tried,  but 
the  former  has  been  used  to  the  entire  exclusion  of  the  other. 


Plaster      / 


7  Girder  Rail 
Scoria  Block 


— 0 


Plaster 


l&TClass  ..- 
Concrete 


Section    A- 5  Section  C-D 

FIG.  168. — Underground  conduit  system. 

In  the  underground  conduit  system,  as  installed  in  the  two 
cities  named,  the  conductors  are  placed  in  a  continuous  trough  or 
conduit,  as  shown  in  Fig.  168.  They  consist  of  two  T-rails,  one 
positive  and  one  negative,  the  track  not  being  used  for  a  con- 
ductor. These  rails  are  entirely  insulated  from  the  ground  by 


292  THE  ELECTRIC  RAILWAY 

porcelain  insulators.  Connection  is  made  to  the  car  equipment 
through  a  detachable  plow,  which  is  carried  on  one  of  the  trucks, 
and  has  on  its  lower  end  a  pair  of  shoes  making  contact  with 
the  two  conductor  rails.  This  system  has  given  excellent  service 
where  it  is  used,  both  in  the  United  States  and  abroad;  the 
principal  objection  is  the  very  high  cost  of  installation. 

Surface  Contact  Systems. — From  time  to  time,  experiments 
have  been  made  with  systems  of  current  supply  which  do  not 
depend  on  overhead  wires,  and  are  less  expensive  to  install  than 
the  underground  conduit.  These  " surface  contact"  systems  all 
operate  by  having  a  series  of  contact  studs,  insulated  from  the 
ground,  but  placed  practically  flush  with  the  street  surface. 
These  studs  are  normally  not  in  the  feeder  circuit;  but.  may  be 
connected  by  a  series  of  magnetic  or  of  mechanical  switches, 
operated  automatically  by  the  passage  of  a  car  in  such  a  manner 
that  only  those  studs  under  it  are  energized.  Current  is  col- 
lected by  some  form  of  shoe  or  "skate"  of  metal  connected 
to  the  car,  and  rubbing  on  the  contact  studs. 

Owing  to  the  great  difficulty  of  maintaining  the  insulation 
of  the  studs,  and  keeping  in  operation  a  large  number  of  auto- 
matic switches,  the  failure  of  any  one  of  which  will  either  leave 
the  car  stalled  or  else  allow  a  live  contact  to  remain  unpro- 
tected, the  systems  of  this  type  have  never  been  popular.  Al- 
though there  are  a  few  lines  of  surface  contact  road  in  opera- 
tion, its  use  is  not  being  extended;  and  in  nearly  all  of  the  places 
where  it  has  been  tried  it  has  been  abandoned  in  favor  of  the 
overhead  trolley  or  of  the  underground  conduit  system. 

The  Return  Circuit. — In  a  constant  potential  circuit,  the 
electrical  relations  are  the  same  on  either  side  of  the  line.  When 
the  system  is  ungrounded,  the  conductors  may  be  made  the  same 
in  cross-section,  and  the  drop  in  potential  will  be  evenly  dis- 
tributed. This  is  the  case  with  the  double-trolley  construction, 
which  is  used  in  a  few  places  in  this  country  and  abroad,  and  in 
the  underground  conduit  system  as  installed  in  New  York  and 
Washington.  In  these  the  outgoing  and  the  return  circuits  are 
made  identical,  and  the  losses  are  evenly  divided  on  the  two 
sides.  There  is  no  reason,  save  for  convenience,  why  they  should 
be  thus  distributed. 

Use  of  Rails  as  a  Conductor. — In  any  railway,  it  is  necessary 
to  use  rails  of  iron  or  steel  for  the  track.  Even  in  the  lightest 
section,  these  form  an  excellent  conductor  if  properly  connected 


THE  DISTRIBUTING  CIRCUIT 


293 


together,  and,  if  there  is  no  objection  to  operation  on  a  grounded 
circuit,  furnish  a  simple  means  of  obtaining  one  of  the  main 
conductors  of  the  electric  system.  The  contact  between  the  rail 
and  the  electrical  apparatus  on  the  car  is  universally  made 
through  the  wheels,  the  motors  and  other  equipment  being 
grounded  to  the  axles.  In  this  way  a  moving  contact  at  least 
equal  to  that  between  the  contact  line  and  the  collecting  device 
can  be  maintained  without  expense. 

Track  Bonding. — In  order  to  utilize  the  track  for  one  of  the 
main  conductors,  it  is  necessary  that  a  complete  electric  circuit 
be  maintained  through  it.  Although  ordinary  track,  when 
newly  laid,  may  be  a  fairly  good  conductor,  it  deteriorates 
rapidly  through  rusting  at  the  rail  joints,  and  the  resistance  be- 
comes so  high  that  the  loss  is  excessive.  To  prevent  this  con- 


FIG.  169. — Chicago  type  unprotected  rail  bond. 

dition  arising,  it  is  customary  to  make  a  permanent  electrical 
connection  between  the  ends  of  each  pair  of  abutting  rails.  This 
process  is  known  as  "bonding"  the  track. 

The  early  electric  roads  were  operated  without  bonding,  until 
it  was  found  that  the  power  stations  could  not  supply  enough 
energy  to  properly  drive  the  cars.  On  discovering  the  cause, 
bonds  of  iron  wire  of  light  section  were  used;  but  these  did  not 
make  the  track  resistance  low  enough  for  successful  operation. 
They  have  been  superseded  by  bonds  of  copper  wire  or  flexible 
strap,  permanently  fastened  to  the  rails.  The  simplest  type  of 
bond  in  use  consists  of  a  piece  of  heavy  copper  wire,  riveted 
through  holes  drilled  in  the  rails  far  enough  from  the  ends  to 
make  the  connection  outside  the  splice  bars.  This  type  of  bond 
is  fairly  satisfactory,  but  in  practice  it  has  been  found  better  to 
use  a  special  terminal  on  the  wire,  as  shown  in  Fig.  169,  which  can 
be  expanded  into  the  holes  in  the  rails,  instead  of  riveted.  This 
makes  a  better  mechanical  connection,  and  prevents  the  entrance 


294  THE  ELECTRIC  RAILWAY 

of  water  into  the  junction,  so  that  there  is  less  liability  of  rusting 
and  deterioration  of  the  bond.  Bonds  of  this  type  are  open  to  a 
serious  commercial  objection,  in  that  they  are  a  constant  tempta- 
tion to  copper  thieves.  To  prevent  this  trouble,  bonds  are  more 
frequently  installed  beneath  the  splice  bars,  where  they  are  pro- 
tected. A  bond  of  this  type  is  shown  in  Fig.  170. 


FIG.  170.— Protected  rail  bond. 

A  type  which  has  been  used  to  some  extent  is  the  soldered 
bond.  This  is  held  to  the  rail  by  soft  soldering,  so  that  no  drill- 
ing is  required.  It  is  difficult  to  solder  coppper  to  steel,  and  there 
is  always  danger  of  imperfect  joints,  which  will  break  after  a 
short  period.  On  this  account  it  has  not  been  very  popular. 

A  method  of  bonding  which  has  met  with  considerable  favor  is 
to  weld  the  bond  terminals  directly  to  the  rails,  by  a  method  like 

,    ...  Electricalfy  drated  Joints 

y  \  "•••-. 


FIG.  171. — Electrically  welded  bond. 

The  soldered  type  bond  is  precisely  similar  in  appearance;  the  difference  is  that  the  joints 
between  the  rail  and  the  bond  are  made  with  soft  solder. 

that  used  for  resistance  welding  of  track.  The  equipment  is 
almost  identical,  but  is  of  smaller  capacity.  The  connection  is 
very  similar  to  a  brazed  joint,  and  can  be  made  entirely  permanent 
if  care  is  used.  This  type  of  bond  (Fig.  171)  is  not  subject  to 
deterioration  as  with  the  expanded  terminal  type.  It  is  some- 
what more  expensive  to  install;  and,  like  the  track  weld,  must  be 
done  by  special  machinery.  If  a  bond  fails  after  the  welding 


THE  DISTRIBUTING  CIRCUIT  295 

equipment  has  been  removed  replacement  is  difficult;  otherwise 
it  is  exceedingly  satisfactory. 

Resistance  of  the  Return  Circuit. — When  the  track  is  used 
as  the  return  circuit,  it  is  important  to  know  its  electrical  qualities. 
Ordinary  steel  has  a  conductivity  of  about  one-twelfth  that  of 
copper,  so  that  a  rail  weighing  100  Ib.  per  yd.  has  a  resistance  of 
about  0.05  ohms  per  mile;  and,  since  there  are  two  rails  which  may 
be  placed  in  parallel  in  each  track,  the  total  per  mile  is  0.025  ohms. 
To  this  must  be  added  the  resistance  of  the  bonds.  These  are 
about  equivalent  in  section  to  a  4-0  copper  wire,  but  there  is  a 
certain  additional  loss  in  the  contact  between  steel  and  copper. 
While  the  total  resistance  of  bonds  varies  greatly,  being  least  for 
the  welded  type,  it  may  ordinarily  be  taken  as  about  0.005 
ohms  per  mile  of  single  rail,  with  joints  every  30  ft.  This  makes 
the  total  resistance  per  mile  of  single  track,  laid  with  100-lb. 
rails,  about  0.0275  ohms.  For  other  weights  of  rail,  the  values 
will  be  proportional,  except  that  the  effect  of  the  bonds  is  con- 
stant. The  resistance  of  the  two  rails  of  a  track,  with  ordinary 
bonding,  as  a  function  of  the  weight,  is  shown  in  Fig.  167.  In 
case  the  bonding  is  not  well  maintained,  the  track  resistance  may 
be  materially  greater. 

Reactance  of  Rails. — When  alternating  current  is  employed 
for  the  propulsion  of  trains,  the  track  being  used  for  the  return 
conductor,  an  additional  effect  is  noticed.  There  is  an  extra 
drop  in  the  circuit  due  to  the  reactance  of  the  rails.  These, 
being  of  a  magnetic  material,  have  a  relatively  high  inductance, 
and  also  cause  "skin  effect"  even  with  fairly  low  frequencies. 
The  values  which  have  been  obtained  in  tests  on  the  flow  of 
alternating  current  in  rails  are  not  entirely  satisfactory,  al- 
though a  great  deal  of  experimental  data  has  been  taken.  The 
best  results  published  are  probably  those  of  the  Electric  Railway 
Test  Commission.1  The  reactance  changes  with  the  current 
carried,  due  largely  to  variations  in  permeability.  In  any  case 
the  "apparent  resistance"  (impedance)  is  several  times  the 
true  resistance  of  the  rail  when  transmitting  direct  current. 

Defects  in  the  Return  Circuit. — The  conductivity  of  good 
track  is  so  high  that  there  is  a  comparatively  small  drop  in 
potential  in  carrying  the  current.  In  a  single  track  with  100-lb. 
rails  this  is  but  2.75  volts  per  mile  per  100  amp.  With  this  value, 

1  Report  of  the  Electric  Railway  Test  Commission,  Chapter  VI,  p.  387; 
McGraw  Publishing  Co.,  New  York,  1906. 


296  THE  ELECTRIC  RAILWAY 

it  is  evident  that  very  little,  if  any,  additional  feeder  capacity 
is  required  unless  the  load  is  exceedingly  large.  But  if  there  are 
a  few  bad  bonds  in  the  track,  all  the  current  may  be  forced  to 
flow  through  one  rail,  thus  increasing  the  drop.  To  obviate  this 
difficulty,  it  is  customary  to  cross-bond  the  rails  at  frequent  in- 
tervals by  connecting  jumpers  to  them,  as  shown  in  Fig.  172. 
With  this  arrangement  the  distance  the  current  will  have  to  flow 
through  one  rail  alone  is  limited  to  the  portion  between  cross- 
bonds  containing  the  bad  connection;  and,  if  there  are  several 
open  bonds  in  the  track,  the  chances  of  its  electrical  continuity 
being  broken  are  very  much  reduced. 

The  result  of  increased  resistance  of  the  track  circuit  is  seen 
at  once  in  the  greater  loss.  The  value  of  the  energy  may  be 
measured  in  dollars  and  cents;  and  only  a  little  calculation  is 
needed  to  show  that  it  is  financially  the  proper  thing  to  keep  the 
return  circuit  in  first-class  condition. 


rCro&s  bonding                                                           Track  Kails                                   \ 

^  Copper  Feeder  Buried  in  Roadbed  '•• 

r  * 

Track  Kails '  Cross 

/  Bonding  •'' 


FIG.  172. — Cross  bonding  with  return  feeder. 

Electrolysis. — There  is  another  disadvantage  from  having 
a  high  resistance,  which  is  even  more  serious,  and  which  cannot 
be  directly  measured  in  the  money  cost.  This  is  the  damage  to 
property  caused  by  electrolytic  action.  The  track  is  normally 
partially  insulated  from  the  earth,  especially  in  dry  weather; 
but  it  must  be  considered  as  a  grounded  circuit  at  all  times. 
Since  the  track  is  in  connection  with  the  soil,  either  partially 
or  completely,  the  latter  becomes  an  electric  conductor  in 
parallel  with  the  rails.  Its  resistance  is  high,  but  not  enough  so 
to  prevent  some  current  flowing  through  it.  If  this  can  be 
determined,  it  is  possible  to  calculate  the  proportion  of  the 
current  which  will  flow  through  the  ground;  but  local  condi- 
tions vary  so  greatly  that  it  is  difficult  to  compute  it  accurately. 
The  use  of  the  earth  as  a  conductor  in  parallel  with  the  track  is 
not  inherently  a  disadvantage,  since  the  effect  is  to  increase 
the  conductivity  of  the  return  circuit,  but  the  difficulty  lies  in 
controlling  the  path  of  the  current  as  it  flows  through  the  ground. 


THE  DISTRIBUTING  CIRCUIT  297 

Earth  conduction  is  electrolytic  in  its  nature.  The  soil  consists 
of  inert  matter,  holding  a  certain  proportion  of  metallic  salts 
which  may  be  in  solid  form,  and  a  content  of  water,  more  or 
less  impregnated  with  solutions  of  salts.  When  current  enters 
the  earth,  the  effect  is  to  eat  away  the  metal;  and  where  it 
leaves  the  ground,  a  metal  or  hydrogen  will  be  deposited.  If 
the  earth  circuit  were  made  up  of  an  iron  salt,  the  effect  would  be 
to  dissolve  a  certain  amount  of  iron  from  the  rail  at  the  point 
where  the  current  enters  the  ground,  and  to  deposit  an  equal 
quantity  of  iron  where  the  current  leaves.  This  would  result 
in  a  certain  weight  of  metal  being  worn  away  from  the  rails  at 
definite  points,  which,  although  a  serious  matter,  concerns  no 
one  but  the  railroad  company.  The  deposition  of  metal  on  the 
rail  at  another  place  would  have  but  little  effect,  since  it  could 
not  aid  the  rail  section  to  any  extent. 

The  main  difficulty  with  earth  conduction  is  that  in  cities 
there  are  many  lines  of  pipe  and  cable  running  parallel  with  the 
railway  tracks,  buried  beneath  the  paving  of  the  streets  through 
which  the  tracks  run.  Such  lines  furnish  a  conducting  medium 
which  is  superior  to  the  earth;  and  the  effect  is  for  the  current 
to  be  diverted  to  them  whenever  there  is  any  tendency  for  it 
to  leave  the  rails.  A  pipe  line  lying  parallel  to  the  track  in- 
creases the  ability  to  take  current  from  the  rails  in  proportion 
to  its  conductivity,  so  that  the  tendency  to  have  current  flow 
through  outside  paths  is  increased  greatly  by  the  presence  of 
such  conductors.  When  the  current  does  flow  through  them,  the 
same  phenomena  occur  as  when  it  leaves  the  rail.  At  the 
point  where  the  current  enters  the  conductor  there  is  a  deposit, 
usually  of  hydrogen,  and  where  it  leaves,  the  metal  is  eaten  away. 
The  amount  which  will  be  eaten  is  a  function  of  the  current  and 
the  time.  One  ampere,  flowing  continuously  for  a  year,  will  dis- 
solve 13.4  Ib.  of  iron  in  the  ferric  state  (trivalent),  20.1  lb.  of 
ferrous  (bivalent)  iron,  or  74.5  lb.  of  lead.  Corrosion  is  likely 
to  take  place  to  a  greater  extent  than  indicated  by  these  values, 
since  the  electrolytic  action  will  induce  natural  corrosion  by  the 
salts  in  the  soil.  The  effect  is  rendered  more  serious  since  the 
tendency  is  for  the  current  to  cause  deep  pits  in  the  metal,  some- 
times eating  through  pipes  in  a  few  spots  when  the  remainder  of 
the  surface  is  but  slightly  affected. 

Remedies  for  Electrolysis. — Since  the  track  is  earthed,  and 
the  ground  furnishes  a  path  in  parallel  with  the  rails,  it  is  not 


298  THE  ELECTRIC  RAILWAY 

possible  to  entirely  eliminate  electrolytic  action  so  long  as  they 
are  employed  for  a  conductor.  The  only  absolute  preventive 
is  to  use  an  insulated  return  circuit.  In  that  case  electrolysis 
cannot  exist.  But  the  excellence  of  the  track  as  an  electric 
conductor  makes  it  most  desirable  to  employ  it  for  conducting 
the  current.  There  are  several  methods  for  mitigating  the 
effects  of  electrolysis,  while  at  the  same  time  permitting  the  use 
of  the  rails  as  part  of  the  electric  circuit. 

The  simplest  way  of  preventing  electrolysis  is  to  cover  the 
parallel  lines  of  pipe  and  other  conductors  with  a  protective  coat- 
ing, which,  if  it  could  be  thoroughly  applied,  and  be  permanent, 
would  be  a  most  effective  remedy.  Unfortunately,  it  is  not 
possible  to  commercially  cover  pipe  with  a  perfect  coating;  and, 
even  if  a  proper  coat  could  be  made,  it  would  be  subject  to 
deterioration  in  contact  with  the  soil.  The  general  method  of 
failure  of  such  a  form  of  protection  is  by  its  breaking  in  a  few 
places.  This  has  the  effect  of  localizing  the  electrolysis,  causing 
more  rapid  destruction  at  such  points  than  if  no  coating  were 
used. 

Another  method  which  has  been  advocated  to  some  extent 
is  to  break  the  pipe  into  sections  by  the  use  of  insulated  joints. 
This  makes  it  a  much  poorer  conductor  than  otherwise.  With 
this  arrangement,  the  current  has  a  tendency  to  follow  the  pipe 
as  far  as  it  is  a  continuous  conductor,  and  to  pass  into  the  earth 
around  the  insulated  joint  and  back  into  the  pipe,  thus  causing 
electrolytic  action  at  such  points.  These  joints  are  somewhat 
expensive,  and  this  method  of  protection  is  only  good  in  com- 
bination with  others. 

Since  the  current  inherently  seeks  the  best  conductor,  and 
hence  tends  to  follow  a  pipe  line,  an  effective  remedy  should 
be  to  make  the  pipe  as  good  a  conductor  as  possible,  by  bonding 
the  joints,  and  attaching  it  to  the  rail  at  suitable  points.  This 
is  often  referred  to  as  the  "pipe  drainage  system."  This  makes 
the  pipe  line  an  integral  part  of  the  electric  circuit,  and  eliminates 
the  chance  of  electrolytic  conduction.  It  leads  to  much  greater 
currents  in  the  pipes  than  when  no  connection  is  used,  and  may 
have  injurious  effects  if,  for  any  reason,  a  bond  is  broken.  In 
such  an  event  the  electrolysis  is  locally  much  worse  than  if  no 
remedy  is  used. 

The  effectiveness  of  the  pipe  drainage  system  is  considerably 
improved  if  a  series  of  negative  feeders  is  installed  to  aid  the 


THE  DISTRIBUTING  CIRCUIT 


299 


rails.  This  tends  to  remove  the  injurious  action  when  a  single 
bond  is  defective,  and  to  reduce  the  drop  of  potential  in  general, 
as  shown  in  Fig.  173.  In  any  case  it  is  difficult  to  determine 
the  proper  feeder  capacity,  since  the  entire  circuit  is  grounded, 
and  the  calculation  of  the  drop  through  parallel  circuits  is 
involved. 

In  order  to  have  this  method  of  protection  effective,  all  pipes 
which  are  in  the  immediate  vicinity  of  the  railway  track  must  be 
connected  to  it,  and  must  be  electrically  continuous.  If  this 
is  done,  there  is  some  additional  danger  to  other  pipes  which 
are  not  connected  to  the  return  system. 

Jo  Trolley 


1  Substation 
To  Negative  Bus 

Track.  Kails 

Pipe  Line 

Cross  foncf 

Track  Rails 

Distance  from  Substation 


FIG.  173. — Potential  drop  with  pipe  drainage  system. 

This  arrangement  is  used  for  prevention  of  electrolysis  in  a  number  of  large  city  systems. 

It  is  evident  that  any  method  of  protection  which  reduces  to 
a  minimum  the  difference  of  potential  between  points  in  the 
track  will  lessen  the  tendency  for  current  to  flow  in  paths  ex- 
terior to  the  regular  circuit.  Such  a  condition  can  be  obtained 
by  the  use  of  insulated  track  feeders,  proportioned  in  a  manner 
similar  to  the  feeding  system  for  the  distributing  circuit.  If 
the  number  and  resistances  of  such  feeders  be  properly  chosen, 
the  difference  of  potential  between  various  points  can  be  re- 
duced to  any  desired  value.  In  order  to  have  such  systems  ef- 
fective, the  feeders  must  be  entirely  insulated  from  the  rails 
except  at  the  points  of  connection.  In  certain  cases,  if,  the  track 
is  tied  to  the  generator  at  the  station  with  a  short,  low-resistance 
cable,  it  may  be  necessary  to  use  feeders  to  other  parts  of  the 


300 


THE  ELECTRIC  RAILWAY 


system  which  are  larger  than  warranted  by  the  economics  of  the 
situation.  This  may  be  obviated  by  removing  the  direct  con- 
nection at  the  station  entirely,  or  by  increasing  its  resistance  until 
the  desired  effect  is  obtained  (see  Fig.  174).  If  some  of  the 
feeders  are  long,  boosters  may  be  inserted,  as  is  sometimes  done 
in  the  distributing  circuit. 

All  of  the  above  methods  have  been  used  for  the  mitigation 
of  electrolysis.  At  the  present  time  there  is  no  general  agree- 
ment that  one  is  decidedly  better  than  the  others.  The  two 
which  have  been  used  to  the  greatest  extent  are  pipe  drainage  and 

To  Trolfey 


Substation 

Jo  Negative  Bus 


Track  Raif& 


Track  Raife 


Insulated  Feeder  I 


FIG.  174. — Potential  drop  with  insulated  negative  feeders  of  correct 

resistance. 

This  method  of  electrolysis  mitigation  is  recommended  by  the  United  States  Bureau  of 
Standards. 

the  insulated  feeder  system.     A  possible  solution  is  the  com- 
bination of  these  two. 

Polarity  of  the  Direct-Current  Circuit. — Until  now  nothing 
definite  has  been  said  about  the  proper  direction  of  current  flow 
in  -direct-current  railway  systems.  So  far  as  electrolytic  effects 
go,  either  the  positive  or  the  negative  terminal  of  the  generator 
may  be  connected  to  the  distributing  circuit;  for,  if  any  current 
goes  out  of  the  rails, it  must  return  at  some  other  point;  and  it  is 
where  the  current  leaves  the  metallic  conductor  that  the  destruc- 
tive effect  occurs.  There  is  this  difference:  if  the  distributing 
circuit  is  connected  to  the  positive  terminal  of  the  generator, 
the  electrolysis  of  the  rail  will  occur  at  the  point  farthest  from 


THE  DISTRIBUTING  CIRCUIT  301 

the  station,  and  of  the  pipes  or  other  structures  nearest  it ;  while 
if  the  distributing  circuit  is  connected  to  the  negative  pole,  the 
pipes  will  be  attacked  farthest  from  the  station  and  the  rails 
will  be  affected  at  the  point  near  it.  Apparently,  since  the  amount 
of  metal  dissolved  is  a  function  of  the  current,  there  is  no  inherent 
difference  in  the  two  methods  of  connection.  Experience  has 
shown,  however,  that  the  current  flow  to  or  from  the  rail  at  the 
points  far  from  the  station  will  be  distributed  over  a  consider- 
able distance,  while  nearby  it  will  be  concentrated  in  a  short 
space.  Since  electrolysis  of  the  rail  only  affects  the  railway  com- 
pany, it  is  the  pipe  line  which  must  be  protected;  and  it  is  easier 
to  inspect  a  short  length  of  pipe  in  the  vicinity  of  the  station, 
and  renew  it  when  necessary,  than  to  take  care  of  a  long  sec- 
tion at  an  indefinite  distance.  For  this  reason,  all  electric 
railways  have  for  many  years  adopted  the  practice  of  making 
the  rail  circuit  negative,  thus  localizing  the  damage.  With  a 
better  understanding  of  the  causes  and  results  of  electrolysis, 
more  effective  remedies  have  been  developed,  so  that  the  need 
for  keeping  the  same  polarity  is  less;  but  in  the  intervening 
time  the  practice  has  been  so  standardized  that  it  is  in  universal 
use  where  direct  current  is  employed  for  train  propulsion. 

Alternating  Currents  and  Electrolysis. — The  above  discussion 
on  electrolysis  has  been  confined  to  a  consideration  of  the  effects 
of  direct  currents.  A  number  of  experiments  have  been  con- 
ducted to  determine  whether  similar  results  are  obtained  when 
alternating  currents  are  used  for  train  propulsion  with  a  grounded 
return.  Up  to  date  the  indications  of  such  tests  have  been 
negative,  there  being  no  evidence  that  any  electrolysis  results 
from  the  alternating-current  circuit.  This  would  naturally  be 
the  case  since  the  reversal  of  the  current  is  so  rapid  that,  even 
if  metal  should  be  dissolved  in  one  alternation,  it  would  be  re- 
placed on  the  electrode  during  the  succeeding  half  cycle. 

Natural  Corrosion. — In  making  tests  to  determine  the  exact 
amount  of  electrolytic  corrosion  it  is  difficult  to  obtain  accurate 
results.  Any  practical  tests  must  necessarily  mean  leaving  metal 
plates  in  the  soil,  exposed  to  the  action  of  the  electric  current. 
Under  such  conditions  there  is  invariably  some  action  due  to  the 
natural  corrosion  of  the  metal  in  contact  with  the  earth  salts. 
Some  recent  tests1  indicate  that  the  rate  of  corrosion  under  such 

1  E.  M.  SCOFIELD  and  L.  A.  STENGER:  "Corrosion  of  Metals  in  Natural 
Soils,"  Electric  Railway  Journal,  Vol.  XLIV,  p.  1092,  Nov.  14,  1914. 


302  THE  ELECTRIC  RAILWAY 

circumstances  is  much  greater  than  was  formerly  imagined. 
Corrosion  may  be  due  to  impurities  in  the  metals  in  contact  with 
the  soil.  Different  soils  have  diverse  activities  in  corroding 
metals;  and  sometimes  when  two  kinds  of  soil  are  in  contact  with 
a  single  piece  of  metal  the  corrosion  is  increased  over  that  in  a 
homogeneous  earth.  The  corrosion  noted  in  some  tests  is  suffi- 
cient to  explain  fully  all  the  phenomena  observed  in  connection 
with  what  is  supposed  to  be  electrolysis  from  current  passing 
through  metals  in  contact  with  the  earth. 

Special  Methods  of  Feeding. — At  various  times,  special 
methods  of  feeding  have  been  suggested,  and  some  of  them  have 
been  used  in  a  few  cases.  A  favorite  suggestion  in  the  early  days 
of  electric  railway  history  was  to  use  the  two  contact  wires  of  a 
double-track  road  as  the  two  outside  lines  of  a  three-wire  system, 
the  track  being  the  neutral.  The  arrangement  of  circuits  is 


Amp  ' 

s 

£?*?'*      Trolley? 

'"Generators  in  Series 
or  Three  -rtlre                                        Car  on 
••'"      (xnera-hr                                             Track  I 

\ 

\  200  Amp. 

Car  -on.  ... 
Track  2  IT 

\  159  Amp 

Track  1                                      I 

<  — 

. 

+  —  50  Amp.                        Cross-  bond  --r^r 

Track  2                                T 

—  -  ->-    150  Amp. 

FIG.  175. — Three-wire  distribution  system. 

In  this  system  the  two  trolley  wires  are  made  the  opposite  sides  of  the  circuit,  and  the 
track  the  neutral.  Note  that  the  current  flowing  through  the  track  is  considerably  smaller 
than  that  in  the  trolley  wires. 

shown  in  Fig.  175.  By  this  means  the  current  flowing  in  the  track 
would  be  reduced  to  that  necessary  for  supplying  the  unbalance 
of  the  system,  and  electrolytic  effects  would  be  eliminated. 

In  a  three-wire  system,  the  neutral  carries  but  a  small  current, 
and  hence  its  size  may  be  much  less  than  that  of  the  outside  wires. 
The  effect  of  making  the  rail  the  neutral  is  to  almost  entirely  lose 
the  advantage  of  its  high  conductivity  as  an  aid  to  the  distributing 
circuit,  so  that  the  decrease  in  the  amount  of  copper  required 
over  the  two- wire  system  with  grounded  return  is  quite  small. 
The  extra  complication  of  the  contact  conductors,  requiring  those 
of  opposite  polarity  to  be  insulated  from  each  other,  makes  cross- 
ings and  switches  difficult  to  lay  out,  and  necessitates  the  use  of 


THE  DISTRIBUTING  CIRCUIT  303 

special  insulators.  Further,  it  makes  the  connection  of  all  the 
overhead  lines  into  a  single  network  impossible,  and  may  prevent 
the  operation  of  a  damaged  section  by  feeding  from  adjacent 
parts  of  the  circuit. 

The  use  of  higher  working  potentials  has  been  advocated  for 
many  years,  and  there  has  been  a  notable  advance  in  this  respect. 
The  first  electric  railways  were  operated  on  100  volts,  or  there- 
abouts; from  that  time  a  rapid  increase  was  made  until  450  volts 
was  used  on  the  Richmond  road  in  1888.  That  potential  was 
adopted  as  being  the  highest  for  which  a  practical  direct-current 
generator  could  be  built.  Since  that  time  the  increase  has  been 
slower,  but  the  pressure  has  gradually  been  brought  up  to  600 
volts,  which  is  now  almost  a  universal  standard.  In  some  few  in- 
stances roads  have  been  built  for  pressures  from  650  to  750  volts, 
which,  until  a  few  years  ago,  represented  the  limit  of  commutator 
design. 

Quite  recently,  the  possibility  of  using  two  or  more  commu- 
tators in  series  has  been  exploited  in  the  so-called  "1200-volt" 
system,  which  in  its  original  conception  contemplated  the  use  of 
two  standard  railway  motors,  insulated  for  the  higher  potential, 
connected  permanently  in  series  on  a  1200-volt  circuit.  The 
generating  equipment  similarly  consisted  of  two  standard  600- 
volt  machines  in  series.  The  effect  of  this  increase  of  line  poten- 
tial is  to  reduce  the  amount  of  distribution  copper  for  the  same 
loss  in  inverse  proportion  to  the  square  of  the  potential;  so  that 
for  two  lines  of  equal  capacity,  one  for  1200  volts  would  require 
but  one-fourth  as  much  copper  in  the  distributing  circuit  as  the 
other  at  600  volts.  Better  knowledge  of  commutation  and  the 
use  of  interpole  machines  has  made  possible  the  construction  of 
motors  and  generators  carrying  1200  volts  on  a  single  commu- 
tator, so  that  the  apparatus  has  been  simplified.  Further  than 
this,  it  has  allowed  the  placing  of  two  of  these  machines  in  series 
on  a  2400-volt  circuit. 

Further  increases  in  the  contact  line  potential  depend  on  the 
development  of  motors  adapted  to  commutate  high  pressures. 
It  is  interesting  to  note  that  the  most  recent  installation,  that  of 
the  Chicago,  Milwaukee  and  St.  Paul,  contemplates  the  use  of 
two  direct-current  motors  in  series  on  a  trolley  at  a  potential  of 
3000  volts.  Laboratory  tests  involving  the  use  of  still  higher 
potentials  show  that  such  increases  are  within  the  limits  of 
possibility. 


304  THE  ELECTRIC  RAILWAY 

When  alternating  current  is  used  on  the  contact  line,  there  is 
no  definite  limit  to  the  pressure  that  can  be  employed,  for  lower- 
ing transformers  give  any  desired  potential  for  the  operation  of 
the  equipment.  The  limit  is  then  only  in  the  pressure  for  which 
the  contact  line  and  the  collectors  can  be  insulated.  Pressures 
of  11,000  volts  to  20,000  volts  are  now  being  used,  but  there  is  no 
reason  why  they  should  not  be  increased  if  found  desirable. 


CHAPTER  XIII 
SUBSTATIONS  FOR  ELECTRIC  RAILWAYS 

Historical  Sketch  of  Development. — Early  electric  railways 
had  the  simplest  of  electrical  circuits.  The  generators  pro- 
duced directly  the  e.m.f.  required  for  operating  the  car  motors, 
and  fed  into  the  contact  line,  usually  without  the  aid  of  an 
auxiliary  feeder  system.  This  arrangement  has  the  sole  ad- 
vantage of  simplicity.  In  every  other  respect  it  is  deficient. 
With  the  growth  of  electric  railways,  it  was  soon  found  that 
the  limitations  imposed  by  this  arrangement  were  serious.  At 
the  outset,  the  efficiency  of  the  distribution  became  low,  on 
account  of  the  excessive  fall  of  potential  in  the  contact  line.  The 
obvious  remedy  was  to  increase  the  area  of  the  conductor,  but  this 
has  the  effect  of  augmenting  the  fixed  charges  on  the  investment. 
In  the  larger  systems,  an  attempt  was  made  to  improve  the 
economy  without  excessive  cost  of  distribution  copper  by  using  a 
number  of  independent  power  stations,  located  at  such  points  as 
would  cut  down  the  length  of  circuit  fed  from  any  one  of  them 
to  a  minimum.  While  this  made  a  decided  improvement  in  the 
economy  of  the  system,  the  result  was  to  have  a  number  of 
small  and  relatively  inefficient  plants,  each  operating  at  a  low 
load  factor.  Various  arrangements  to  better  this  condition 
were  tried,  such  as  the  use  of  boosters  on  long  feeders;  but  these 
remedies  did  not  get  to  the  root  of  the  trouble. 

The  beneficial  effects  on  the  distribution  circuit  of  the  use  of 
higher  potentials  was  early  demonstrated;  but  it  was  not  found 
possible  to  increase  the  capacity  of  a  single  commutator  beyond 
a  limiting  e.m.f  of  about  550  to  650  volts.  This  was  (and  still 
is,  for  some  classes  of  railway  service)  the  maximum  potential 
that  could  be  applied  successfully  to  the  contact  line.  The  diffi- 
culties of  distribution  were  found  greatest  in  interurban  roads, 
where  the  length  of  feeder  circuits  and  the  concentration  of 
the  load  in  a  few  scattered  units  made  the  problem  exceedingly 
difficult  to  handle.  In  order  to  get  away  from  the  limitations 
imposed  by  direct  generation  at  the  contact  line  potential,  the 
20  305 


306  THE  ELECTRIC  RAILWAY 

use  of  a  separate  generating  and  transmission  system  working 
at  a  pressure  considerably  higher  than  that  of  the  distribution 
circuit  was  tried  fairly  early  in  the  history  of  electric  railways. 
This  furnished  a  solution  of  the  problem  which  has  been  entirely 
satisfactory  except  for  the  complications  involved,  and  is  now 
universally  used  for  most  classes  of  electric  railways. 

Complex  Distribution  Systems. — The  use  of  a  high-tension 
transmission  circuit  with  a  low-tension  distribution  system 
requires  the  introduction  of  some  form  of  transforming  ma- 
chinery into  the  electric  circuit,  resulting  in  a  great  flexibility  not 
possible  with  direct  generation.  Generally  speaking,  there  are 
four  possible  combinations  which  may  be  made,  as  follows: 

1.  Generation  of  alternating  current,  and  distribution  as 
alternating  current  at  the  same  frequency. 

2.  Generation  of  direct  current,  and  distribution  as  alter- 
nating current. 

3.  Generation  of  direct  current,  and  distribution  as  direct 
current. 

4.  Generation  of  alternating   current,  and  distribution  as 
direct  current. 

Of  these  four  possible  combinations,  all  except  the  first  re- 
quire the  use  of  some  form  of  rotating  converting  machinery 
(with  the  exception  of  the  mercury  vapor  rectifier).  The  use 
of  the  first  combination  is  limited  to  those  roads  using  alternat- 
ing-current equipment  on  the  cars  and  locomotives,  and  for  this 
class  of  service  is  almost  universally  employed. 

The  second  and  the  third  methods  contemplate  the  use  of 
high-tension  direct-current  transmission.  At  the  present  time 
there  is  but  one  system  available  for  this  form  of  transmission, 
the  Thury  system.  This  consists  of  the  use  of  a  number  of  con- 
stant-current machines  in  series,  both  at  the  generating  and 
at  the  receiving  ends  of  the  transmission  line.  The  motors  at 
the  receiving  station  drive  ordinary  generators  of  the  constant- 
potential  type,  designed  for  the  distributing  circuits  on  which 
they  are  to  operate.  In  Europe,  several  transmission  lines 
of  considerable  length,  and  working  at  maximum  potentials 
of  over  50,000  volts,  are  in  service.  The  system  is  extremely 
simple,  but  is  limited  in  application  on  account  of  its  lack  of 
flexibility.  The  second  combination  would  be  available  for  the 
operation  of  alternating-current  roads,  but  on  account  of  the 


SUBSTATIONS  FOR  ELECTRIC  RAILWAYS      307 

ability  to  employ  stationary  transformers  in  the  first  method,  that 
is  invariably  used  in  practice.  The  third  combination  is  rarely 
seen. 

The  fourth  method  of  transmission  is  the  one  of  widest  applica- 
tion, since  it  allows  the  use  of  standard  alternating-current 
machinery  for  the  transmission  circuit,  and  standard  direct- 
current  apparatus  on  the  distributing  system.  The  conversion 
from  alternating  current  to  direct  can  be  made  in  a  number  of 
ways,  as  explained  in  this  chapter. 

Types  of  Converters. — At  the  present  time,  there  are  several 
methods  available  for  the  conversion  of  alternating  current  into 
direct  current.  They  are: 

1.  The  motor-generator  set. 

(a)  Using  a  synchronous  motor. 

(b)  Using  an  induction  motor. 

2.  The  synchronous  (rotary)  converter. 

3.  The  induction  motor-converter. 

4.  The  permutator. 

5.  The  mercury  vapor  rectifier. 

6.  Various  types  of  mechanical  rectifiers. 

The  motor-generator  set,  the  motor-converter,  and  the 
permutator,  give  direct-current  potentials  which  are  inde- 
pendent of  the  alternating  e.m.f.  The  alternating-current  wind- 
ing may  be  constructed  for  any  desired  potential  within  the 
limits  of  the  machine  insulation,  while  the  direct-current  side 
is  arranged  to  give  any  standard  potential  desired.  The  syn- 
chronous converter,  the  mercury  vapor  rectifier,  and  all  the 
types  of  mechanical  rectifiers,  are  limited  in  their  design  to  a 
fixed  ratio  between  alternating  and  direct  e.m.f. 's.  The  latter 
must  therefore  be  used  in  connection  with  lowering  transformers 
to  give  the  desired  direct  potential. 

Motor-Generator  Sets. — The  simplest  and  most  flexible  type 
of  converting  machinery  is  the  motor-generator  with  an  induc- 
tion motor,  shown  diagrammatically  in  Fig.  176.  The  two  ma- 
chines are  mounted  with  their  rotating  members  on  a  common 
shaft,  but  are  in  all  other  respects  independent.  The  induction 
motor  is  usually  of  the  squirrel-cage  type,  since  the  starting  duty 
is  not  heavy;  and  it  operates  at  high  efficiency  and  practically 
constant  speed  over  the  entire  range  of  load.  The  direct- 
current  generator  may  be  of  any  standard  type,  and  wound 


308 


THE  ELECTRIC  RAILWAY 


for  the  contact  line  potential.  It  can  be  equipped  with  a  shunt 
or  a  compound  field  winding;  and  constant  potential  regulation 
may  be  effected  either  by  the  compounding  of  the  series  field  or 
by  the  use  of  an  automatic  regulator. 


Three-Phase 
Supply 


FIG.  176. — Induction  motor- generator  set. 

In  some  cases  a  shunt-wound  generator,  with  a  potential  regulator,  may  be  used  instead 
of  the  compound-wound  generator  illustrated. 

The  objections  to  the  induction  motor-generator  are  chiefly 
its  high  first  cost,  low  efficiency  as  compared  with  other  forms  of 
converters,  and  the  comparatively  large  lagging  current  which 
is  taken  by  the  induction  motor. 


Three -Phase 
Supply 


fxcifcr 


Synchronous 
Motor 


D.  C.  Oenerafor 


FIG.  177. — Synchronous  motor-generator  set. 

The  synchronous  motor  is  occasionally  excited  from  the  direct-current  generator  when  a 
supply  of  direct  current  is  available  for  starting,  or  when  a  self-starting  motor  is  used. 

The  synchronous  motor-generator,  shown  in  Fig.  177,  removes 
the  objection  of  low  power  factor,  which  is  inherent  to  the  in- 
duction motor.  Exciting  current  is  most  frequently  taken  from 


SUBSTATIONS  FOR  ELECTRIC  RAILWAYS      309 

a  separate  direct-current  generator,  usually  mounted  on  the 
same  shaft  with  the  main  machines,  although  in  some  cases 
direct  current  from  the  main  generator  is  used  for  excitation. 
By  varying  the  exciting  current  the  power  factor  may  be  con- 
trolled within  certain  limits.  The  cost,  weight  and  efficiency  are 
approximately  the  same  as  for  the  induction  motor— generator. 

Synchronous  Converters. — The  synchronous  converter,  in 
effect,  combines  the  armatures  of  the  two  machines  of  the 
synchronous  motor-generator  set.  By  so  doing,  the  e.m.f. 
obtained  at  the  brushes  is  a  fixed  function  of  that  led  into  the 
machine  from  the  alternating-current  side,  making  independent 
regulation  of  the  direct-current  pressure  impossible.  Various 
devices  may  be  introduced  to  remedy  this  defect,  the  simplest  of 
which  is  the  use  of  a  series-wound  synchronous  booster,  through 
which  the  alternating  current  must  pass.  By  exciting  the  field 
of  the  booster  with  the  line  current  of  the  direct-current  side, 
an  additional  e.m.f.  is  added  to  or  subtracted  from  the  potential 
delivered  by  the  transformers.  Another  method  of  regulation 
is  the  use  of  the  split-pole  converter,  in  which  the  ratio  between 
alternating  and  direct  e.m.f.'s  may  be  varied  by  changing  the 
wave  from  within  the  converter  armature.  Neither  scheme 
is  used  in  practice  to  any  extent  for  railway  service,  but  they  are 
valuable  in  connection  with  industrial  applications. 

The  usual  method  of  regulation  is  to  put  a  series  winding  on  the 
converter  field,  as  shown  in  Fig.  178,  similar  to  the  ordinary  series 
field  winding  used  on  compound  direct-current  generators.  In 
connection  with  such  a  winding  reactance  coils,  through  which 
the  main  current  is  drawn,  are  placed  on  the  alternating-current 
side.  The  shunt  field  rheostat  is  set  so  that  the  converter 
draws  slightly  lagging  current  at  no  load.  With  increase  in 
load,  the  series  turns  of  the  field  winding  cause  over-excitation, 
making  the  current  lead  the  e.m.f.  When  this  leading  current 
is  drawn  through  the  inductance  of  the  machine,  the  transformers 
and  the  reactance  coils,  a  reactive  drop  is  produced  which  adds 
to  the  potential  delivered  from  the  circuit.  By  properly  pro- 
portioning the  series  winding  and  the  reactance  coils,  the  potential 
on  the  direct-current  side  may  be  regulated. 

In  large  systems,  where  too  much  leading  current  is  objection- 
able, the  e.m.f.  supplied  the  alternating  side  of  the  rotary  converter 
is  varied  by  some  standard  form  of  potential  regulator,  such  as 
the  induction  regulator.  This  method  may  be  used  alone,  or  in 


310 


THE  ELECTRIC  RAILWAY 


combination  with  the  series  winding  on  the  converter;  so  that 
both  the  direct  e.m.f.  and  the  power  factor  of  the  alternating- 
current  circuit  may  be  governed  at  will.  The  arrangement  is 
similar  to  that  shown  in  Fig.  178,  except  that  the  regulator 
replaces  the  reactance  coils. 

The  early  rotary  converters  were  all  built  for  comparatively 
low  frequencies,  most  of  them  being  for  25  cycles.  Recent  im- 
provements in  design,  especially  the  use  of  interpoles,  have  made 
the  performance  and  the  cost  of  60-cycle  synchronous  converters 
practically  on  a  par  with  those  for  lower  frequencies. 


Three-Phase 

Supply 


FIG.  178. — Synchronous  converter  with  regulating  reactance. 
The  reactance  coils  may  be  replaced  with  an  automatic  potential  regulator. 

The  Motor-Converter. — The  motor-converter,  or  "  cascade- 
converter,"  is  an  application  of  the  same  principle  as  that  used 
in  cascade  control  of  induction  motors.  It  consists,  Fig.  179, 
of  a  primary  winding  like  that  for  an  induction  motor,  and  a 
secondary  of  a  type  similar  to  that  of  the  phase-wound  motor, 
the  principal  difference  being  that  the  converter  is  ordinarily 
designed  for  a  larger  number  of  phases.  The  secondary  winding 
is  tapped  directly  into  the  armature  of  a  machine  electrically 
the  same  as  the  synchronous  converter.  As  in  cascade  operation 
of  motors,  the  motor  end  and  the  converter  end  of  the  set  may 
each  have  any  number  of  poles;  practically  they  are  wound  for 
the  same  number.  For  starting,  the  secondary  winding  of  the 
induction  machine  is  brought  out  to  collector  rings,  through  which 
it  may  be  short-circuited  with  resistance. 


SUBSTATIONS  FOR  ELECTRIC  RAILWAYS      311 

In  operation,  the  set  runs  at  half  the  speed  of  the  primary 
field,  the  frequency  in  the  secondary  being  half  that  of  the  line; 
while  the  converter  operates  as  though  in  synchronism  at  the 
secondary  frequency.  Half  of  the  power  is  transmitted  directly 
through  the  secondary  winding,  while  the  other  half  is  delivered 
through  the  shaft.  The  size  of  the  set  is  therefore  decidedly  less 
than  for  a  motor-generator  of  equal  rating.  The  efficiency  is 
considerably  better  than  that  of  a  motor-generator,  but  slightly 
less  than  of  the  ordinary  rotary  converter.  Synchronizing  is 
extremely  simple,  consisting  in  adjusting  the  starting  resistance 
until  the  machine  falls  into  step.  The  starting  current  is  small; 
but,  on  the  other  hand,  the  magnetizing  current  is  drawn  directly 
from  the  line,  as  in  an  induction  motor,  so  that  the  power  factor 


Three  -Phase 
Supply 


FIG.  179. — Induction  motor-converter. 

The  induction  motor  end  and  the  converter  end  of  the  converter  are  usually  assembled 
within  one  frame;  this  is  not  shown  in  the  diagram. 

is  not  so  easily  controlled.  Over-excitation  of  the  direct-current 
field  will,  however,  reduce  the  quadrature  component  of  the 
primary  current. 

While  the  motor— converter  had,  at  the  time  of  its  introduction, 
considerable  superiority  over  the  synchronous  converter  for 
operation  at  high  frequencies,  recent  improvements  in  the  latter 
have  placed  the  two  machines  about  on  a  par  in  this  respect. 
When  the  motor— converter  can  have  its  primary  wound  for  the 
line  potential,  without  the  use  of  lowering  transformers,  there  is 
little  difference  in  first  cost;  when  transformers  are  required,  the 
motor-converter  will  be  more  expensive.  Its  greatest  advantage 
is  the  small  amount  of  attention  needed  for  operation,  as  compared 
with  the  synchronous  converter. 


312  THE  ELECTRIC  RAILWAY 

The  Permutator. — If  the  secondary  winding  of  an  induction 
motor  is  held  still,  current  will  be  generated  in  it  at  the  frequency 
of  the  primary  circuit,  and  at  an  e.m.f.  equal  to  that  of  the  pri- 
mary, multiplied  by  the  ratio  of  transformation.  If  the  second- 
ary winding  be  connected  to  a  commutator  of  the  ordinary  type, 
and  a  set  of  brushes  rotated  thereon  at  synchronous  speed,  direct 
current  can  be  taken  off  and  used  for  any  purpose.  A  machine 
embodying  this  principle,  known  as  the  permutator,  has  been 
used  for  several  years  in  Europe  for  converting  alternating  cur- 
rent into  direct.  In  its  construction,  the  parts  may  be  arranged 
similarly  to  those  of  the  induction  motor;  but,  since  there  is  no 
relative  motion  between  them,  no  air-gap  is  necessary,  and  by 
omitting  it  the  magnetizing  current  is  reduced.  Brushes  are 
rotated  on  the  commutator  by  means  of  a  small  synchronous 
motor  wound  with  the  same  number  of  poles  as  the  main 
machine. 

The  permutator  is  reported  to  have  excellent  operating  char- 
acteristics. The  efficiency  is  high,  since  the  mechanical  losses 
due  to  rotation  are  almost  entirely  absent;  and  the  weight  and 
cost  are  about  the  same  as  those  of  rotary  converters  of  the 
same  rating.  The  principal  objection  is  due  to  rotation  of  the 
brushes.  This  makes  necessary  a  somewhat  complicated  brush 
rigging,  and  precludes  any  repairs  or  replacement  of  brushes  while 
the  machine  is  in  operation.  The  magnetizing  current,  being 
the  same  in  character  as  that  for  the  induction  motor,  is  lagging; 
and,  notwithstanding  the  quadrature  component  is  less  than  for  a 
motor  of  equal  rating,  it  is  never  possible  to  eliminate  it,  although 
the  power  factor  is  very  high.  The  ratio  between  the  alternating 
and  the  direct  e.m.f.  is  fixed  in  any  one  machine,  but  is  not 
limited  to  a  definite  ratio  as  with  the  synchronous  converter. 
It  is  possible  to  wind  the  machine  for  high  potentials,  as  with 
the  induction  motor  or  the  motor-converter.  With  the  im- 
provement of  other  forms  of  converters,  it  is  doubtful  whether 
the  permutator  will  have  a  wide  application. 

The  Mercury  Vapor  Rectifier. — The  use  of  the  mercury  vapor 
rectifier,  in  connection  with  locomotive  equipment,  has  already 
been  mentioned  in  Chapter  V.  This  apparatus  is  equally 
applicable  for  substation  service.  The  principle  of  operation  is 
based  on  the  fact,  discovered  by  Dr.  Peter  Cooper  Hewitt,  that 
a  mercury  electrode  in  contact  with  the  vapor  of  mercury  will 
conduct  current  in  one  direction  only. 


SUBSTATIONS  FOR  ELECTRIC  RAILWAYS      313 

To  utilize  the  principle  for  rectification  from  a  single-phase 
circuit,  the  terminals  of  the  secondary  winding  of  a  transformer 
(or  of  an  auto-transformer)  are  connected  to  two  electrodes  in  a 
vessel  containing  a  mercury  cathode,  and  vapor  of  mercury  at 
the  proper  pressure.  The  arrangement  of  circuits  is  shown  in 
Fig.  180.  There  is  no  tendency  to  cause  a  flow  of  current  through 
the  vapor  under  such  conditions;  but  when  the  current  is  once 
started,  as  may  be  done  by  providing  a  metallic  conductor  be- 
tween the  electrodes  (for  instance,  by  tilting  the  container  until 
the  mercury  forms  a  continuous  film  between  the  cathode  and 


Tfrree-  Phase 
Supply 


Alternating 
...-•  Current  ' 


Transformer 


Neutral  Wire 


Neutral  Wire 


Steel  Case 

(Insulated  Inside) 

..  -Metallic  Mercury 


_ '  Inductance 

FIG.    180. — Single-phase  mer- 
cury vapor  rectifier. 
The  direct  potential  may  be  varied 
by  connecting  to  different  taps  on  the 
transformer  secondary. 


Steel  Case 
(insulated  Inside) 


Metallic  Mercury 


FIG.  181. — Three-phase  mercury 
vapor  rectifier. 


the  other  electrode),  or  by  means  of  a  motor-generator  set,  the 
vapor  will  continue  to  conduct  current  from  the  anode  (electrode 
connected  to  the  transformer  winding)  to  the  cathode  as  long 
as  the  e.m.f.  persists  in  the  same  direction.  When  it  ceases,  the 
vapor  becomes  a  non-conductor.  If,  however,  current  con- 
tinues to  flow  until  the  e.m.f.  has  established  itself  in  the  proper 
direction  through  the  other  electrode  connected  to  the  trans- 
former, the  current  will  be  maintained  through  the  vapor  in 
the  same  direction  as  before,  but  from  the  other  anode.  With  a 


314  THE  ELECTRIC  RAILWAY 

single-phase  source,  this  can  be  done  if  sufficient  inductance  is 
inserted  in  the  receiving  circuit.  If  the  latter  is  normally  in- 
ductive, as  when  supplying  motors,  no  additional  reactance  is 
needed.  The  other  lead  for  the  direct  current  is  taken  from 
the  neutral  point  of  the  transformer;  and  hence  the  current  flows 
for  one-half  of  the  alternating  cycle  through  one  portion,  and 
for  the  other  half  through  the  remainder,  of  the  winding. 

With  a  three-phase  supply  for  the  alternating  current,  the 
arrangement  is  slightly  different,  as  shown  in  Fig.  181.  There 
is  no  need  of  inductance  to  maintain  the  circuit  through  the 
vapor,  since  two  currents  are  always  flowing  in  the  same  direction. 

Although  the  current  produced  by  the  rectifier  is  unidirectional, 
it  is^not  uniform  in  amplitude.  If  there  were  no  inductance  in 
the  circuit,  the  form  of  the  rectified  current  would  be  very  nearly 
the  same  as  that  of  the  alternating,  with  every  other  half-wave 
reversed.  The  effect  of  inductance  is  to  smooth  out  the  waves  of 
current  until  there  is  only  a  slight  ripple.  For  similar  reasons, 
the  current  produced  from  a  polyphase  rectifier  is  more  uniform 
than  when  a  single  phase  is  used.  Extensive  tests  which  have 
been  made  indicate  that  the  effect  of  inductance  on  the  wave 
form  is  great  enough  that  standard  direct-current  motors  will 
give  entirely  satisfactory  service. 

The  efficiency  of  the  rectifier  is  high  at  commercial  potentials. 
The  loss  appears  to  consist  mainly  of  a  definite  drop  which  is 
independent  of  the  current;  so  that  the  converter  has  a  constant 
efficiency  at  all  loads.  This  drop  of  potential  varies  from  ap- 
proximately 14  volts  in  the  small  rectifiers  used  for  charging 
storage  batteries,  up  to  50  volts  in  some  of  the  larger  units  which 
have  been  tested.  The  rectifier  used  on  the  Pennsylvania  Rail- 
road experimental  equipment  in  19141  showed  a  constant  drop 
of  about  25  volts,  when  delivering  approximately  1200  volts 
direct  current.  The  efficiency  is  hence  in  the  neighborhood  of 
98  per  cent. 

It  must  be  remembered  that  at  the  present  time  (1915)  the 
mercury  vapor  rectifier  is  still  in  the  experimental  state,  but 
apparatus  has  been  built  giving  outputs  as  high  as  1000  kw.  and 
7000  volts.2  Compared  with  other  forms  of  converting  machin- 
ery, it  is  light  in  weight,  low  in  first  cost  and  in  maintenance,  and 
exceptionally  high  in  efficiency.  If  the  development  proceeds 
as  rapidly  as  is  at  present  anticipated,  it  will  certainly  place  the 

1  Electric  Railway  Journal,  Dec.  19,  1914,  Vol.  XLIV,  p.  1343. 

2  Electric  Journal,  January,  1915,  Vol.  XII,  p.  2. 


SUBSTATIONS  FOR  ELECTRIC  RAILWAYS      315 

rectifier  in  an  excellent  position,  both  for  operation  on  locomo- 
tives or  cars,  and  for  permanent  location  in  substations  along 
the  line. 

Mechanical  Rectifiers. — Some  work  has  been  done  in  perfect- 
ing various  forms  of  mechanical  rectifiers.  These  devices  are 
practically  two-part  commutators,  driven  at  synchronous  speed, 
the  brushes  being  placed  in  such  positions  that  they  will  reverse 
the  current  as  the  alternating  wave  is  passing  through  zero.  If 
the  current  and  inductance  remain  constant,  such  a  device  can 
be  made  very  satisfactory.  If,  however,  the  apparent  inductance 
of  the  direct-current  circuit  is  subject  to  rapid  fluctuations,  the 
position  of  the  wave  will  shift;  and,  to  secure  good  commutation, 
the  brushes  should  be  moved  correspondingly.  This  makes  the 
operation  of  the  rectifier  unsatisfactory  in  connection  with  a 
motor  load.  Various  attempts  to  overcome  the  trouble  have 
been  made,  and  results  of  tests  have  been  announced  from  time 
to  time  which  would  indicate  that  satisfactory  rectifiers  have 
been  built ;  but  up  to  the  present  none  has  been  used  commercially 
with  any  large  measure  of  success.  It  is  questionable  whether 
any  device  of  this  type  can  equal  the  performance  of  the 
mercury-vapor  rectifier,  especially  at  high  potentials  and  large 
currents. 

Comparison  of  Converters. — In  the  present  state  of  the  art,  it  is 
exceedingly  difficult  to  give  a  satisfactory  comparison  of  the 
different  forms  of  apparatus  for  converting  alternating  current 
into  direct.  The  excellence  of  the  modern  synchronous  converter 
has  caused  its  adoption  for  practically  all  classes  of  railway 
service,  so  that  motor-generator  sets,  the  induction  motor-con- 
verter, and  the  permutator  may  not  be  used  to  any  extent  in 
competition  with  it.  On  the  other  hand,  the  synchronous  con- 
verter, from  its  inherent  design,  is  difficult  to  construct  for  the 
extremely  high  direct  potentials  which  apparently  will  be  neces- 
sary for  future  development  of  heavy  railway  equipment  if 
direct-current  motors  are  to  be  employed;  and  the  possibilities 
of  rectifiers,  especially  of  the  mercury  vapor  type,  are  so  attractive 
that  the  latter  will  undoubtedly  be  a  serious  competitor  of  the 
synchronous  converter  in  this  field.  It  is,  therefore,  idle  to 
consider  converting  equipment  standardized  at  the  present  time; 
although,  where  heavy  currents  at  comparatively  low  potentials 
are  required,  the  synchronous  converter  is  undoubtedly  the  best 
machine  at  present. 


316  THE  ELECTRIC  RAILWAY 

Substation  Equipment. — With  the  wide  diversity  in  apparatus 
which  may  be  used  for  converting  one  kind  of  current  into 
another,  it  is  not  possible  to  consider  any  form  of  substation 
equipment  as  standard.  The  arrangement  of  apparatus,  using 
synchronous  converters,  has,  however,  been  almost  completely 
standardized.  What  is  desired,  in  order  to  keep  the  operating 
cost  low,  is  a  station  in  which  the  machinery  is  most  nearly 
automatic,  so  that  little  or  no  attention  is  necessary.  With 
modern  machines,  this  is  approximated;  but  with  rotating  de- 
vices, there  is  always  need  for  expert  attention. 

There  is  one  notable  exception:  the  alternating-current  trans- 
former station.  If  alternating  current  is  to  be  used  on  the  con- 
tact line,  all  the  equipment  that  is  required  in  the  substation  is 
the  necessary  installation  of  transformers,  with  proper  switching 
and  protective  devices.  Such  a  station  can  be  made  automatic 
in  operation,  requiring  no  attention  whatever  after  the  line 
switches  have  been  closed,  except  in  case  of  abnormal  conditions. 
If  the  mercury  vapor  converter  is  developed,  as  now  seems  likely, 
it  may  be  possible  to  have  similar  automatic  substations  for 
conversion  from  alternating  to  direct  current. 

Storage  Batteries  in  Substations. — The  widely  fluctuating 
loads  in  ordinary  railway  service  make  it  impossible  to  keep  the 
machines  operating  at  the  most  efficient  load  at  all  times.  There 
are  two  types  of  fluctuation  of  load:  the  regular  daily  changes, 
due  to  the  number  of  trains  in  operation,  and  momentary  varia- 
tions from  trains  starting,  ascending  grades,  etc.  The  former 
can  be  easily  taken  care  of  by  having  the  proper  number  of 
units  in  operation,  starting  and  stopping  them  as  the  load  changes. 
The  latter  cannot  be  cared  for  in  this  manner,  but  will  place  mo- 
mentary overloads  on  the  equipment,  sometimes  amounting  to 
twice  the  full-load  rating  of  the  machines  in  service. 

By  the  use  of  storage  batteries,  these  rapid  momentary  fluc- 
tuations can  be  smoothed  out  to  a  very  large  extent  on  roads 
operating  with  direct  current.  For  such  service  the  battery  is 
either  " floated"  on  the  line,  or  connected  to  it  through  a  suitable 
regulator.  A  sudden  demand  for  current  causes  the  battery  to 
discharge,  so  that  the  additional  load  is  assumed  by  it  instead  of 
by  the  converters.  When  the  load  falls  below  the  average  value, 
the  batteries  are  charged.  In  this  way  the  substation  equipment 
is  kept  operating  at  or  near  its  maximum  efficiency,  and  the  regu- 
lation of  the  transmission  circuit  is  improved. 


SUBSTATIONS  FOR  ELECTRIC  RAILWAYS      317 

The  other  principal  use  of  storage  batteries  in  substations  is  to 
assume  a  portion  of  the  total  load,  so  that  the  excess  capacity 
need  not  be  carried  in  rotating  machines.  This  has  the  effect 
of  reducing  the  cost  of  the  transmission  line  and  of  the  generating 
equipment,  since  the  peak  is  carried  by  the  batteries,  and  does  not 
affect  the  power  station. 

A  third  use  of  the  storage  battery  is  to  assume  the  total  load 
when,  for  any  reason,  the  generating  equipment  is  out  of  service. 
This  makes  it  possible  to  operate  the  road  for  short  periods  in 
case  of  accident  to  the  machinery,  so  that  the  damaged  apparatus 
may  sometimes  be  repaired  and  put  back  in  service  before  the 
battery  is  discharged.  The  battery  may  also  assume  the  entire 
load  during  hours  when  the  service  is  light,  as  at  night. 

It  is  evident  that  the  same  battery  can  be  used  to  serve  all  of 
these  purposes;  but  the  capacity  required  is  very  different  for 
each  of  them.  To  smooth  out  the  momentary  variations  in  load, 
a  comparatively  small  battery  is  needed,  since  the  total  time  of 
charge  and  discharge  is  quite  short  for  a  single  peak  due  to 
starting  a  car.  To  assume  the  daily  overloads  during  the  rush 
hours  a  larger  battery  is  needed,  and  to  assume  the  entire  load  of 
the  station  for  extended  periods  takes  a  still  larger  battery,  the 
exact  size  of  course  depending  on  the  frequency  and  length  of  the 
interruptions  to  be  provided  for. 

It  cannot  be  claimed  that  the  operation  of  storage  batteries  is  in 
itself  efficient,  for  the  conversion  from  electric  into  chemical 
energy  and  back  again  will  result  in  a  considerable  loss.  The 
efficiency  in  this  service  will  ordinarily  be  from  75  to  85  per  cent. 
The  effectiveness  of  the  battery  comes  from  equalization  of  the 
load,  so  that  the  generators,  transmission  and  converters  operate 
with  less  loss. 

The  use  of  batteries  is  not  so  general  at  present  as  it  was  several 
years  ago.  Better  design  of  electrical  machinery  makes  it  more 
able  to  stand  the  momentary  overloads;  and  the  efficiency  of 
modern  equipment  is  high  over  the  entire  range  of  loads.  The 
main  functions  of  the  battery  may  thus  be  served  by  other  means, 
so  that  there  is  not  the  use  for  it  that  formerly  obtained. 

Batteries  can  be  applied  to  alternating-current  roads  with  the 
interposition  of  a  rotary  converter  or  a  motor-generator  to  con- 
nect them  to  the  load.  While  this  arrangement  is  not  widely 
used,  there  is  at  least  one  installation  in  the  United  States  operat- 
ing in  this  manner.  It  is  reported  to  be  entirely  satisfactory. 


318  THE  ELECTRIC  RAILWAY 

Classes  of  Distribution  Systems. — Distribution  circuits  may  be 
classed  into  two  radically  different  forms:  those  in  which  the  sub- 
station may  be  located  at  the  center  of  the  system,  the  lines  ra- 
diating from  it;  and  those  in  which  the  distribution  is  linear,  there 
being  but  one  line,  along  which  the  substation  may  be  located. 
The  former  represents  the  conditions  in  city  service,  or  in  some 
kinds  of  terminal  electrification;  while  the  latter  represents  the 
case  of  the  interurban  road  or  the  trunk  line.  Naturally,  there 
will  be  many  places  in  which  the  two  classes  will  overlap,  so  that 
an  absolute  classification  is  somewhat  difficult.  The  general 
principle  remains  the  same  in  either,  and  the  problems  involved 
are  similar. 

Location  and  Capacity  of  Substations. — The  most  difficult 
problem  in  connection  with  the  distribution  system  is  the  deter- 
mination of  the  proper  positions  for  substations  to  give  the  maxi- 
mum efficiency  in  operation.  The  problem  is  complicated  by  the 
fact  that  the  location  not  only  affects  the  amount  of  feeder  copper 
required  for  a  given  efficiency,  or  the  efficiency  with  a  given 
amount  of  copper,  but  also  changes  the  capacity  of  individual 
stations,  thus  influencing  the  cost.  What  is  desired  from  the 
economic  standpoint  is  to  determine  that  arrangement  which  will 
give  the  lowest  annual  cost  for  losses,  and  interest  and  depreciation 
on  the  investment. 

The  most  general  statement  of  the  proper  arrangement  of  the 
circuit  is  that  known  as  Kelvin's  law,  which  was  developed  by 
Lord  Kelvin  in  connection  with  the  determination  of  conductor 
size  for  transmission  circuits.  This  law  is  usually  stated  as  fol- 
lows: "The  most  economical  conductor  is  that  in  which  the 
annual  cost  of  energy  wasted  (due  to  line  loss)  is  equal  to  the 
interest  and  depreciation  on  the  capital  outlay  that  is  propor- 
tional to  the  weight  of  the  conductor." 

In  practice  it  is  not  possible  to  have  the  conditions  of  Kelvin's 
law  met  at  all  times.  The  law  holds  true,  in  its  strictest  sense, 
only  when  a  given  value  of  current  is  flowing  constantly.  It  has 
been  seen  that  the  current  in  an  electric  railway  transmission  or 
distribution  circuit  is  always  fluctuating  over  a  wide  range.  The 
condition  necessary  for  use  in  connection  with  Kelvin's  law  may 
be  determined  for  all  practical  purposes  by  taking  the  root  mean 
square  value  over  an  extended  period  of  time,  which  will  correctly 
represent  the  average  loss  due  to  the  current,  as  called  for  in  the 
statement  of  the  law. 


SUBSTATIONS  FOR  ELECTRIC  RAILWAYS      319 

In  the  case  of  roads  which  are  of  the  radial  type,  the  location  of 
substations  is  comparatively  simple,  although  the  mathematical 
treatment  is  much  involved.  What  is  required  is  to  have  efficient 
operation,  at  the  same  time  keeping  the  maximum  drop  as  small 
as  possible  consistent  with  economy.  In  such  cases,  the  amount 
of  load  is  ordinarily  sufficiently  great  that  the  capacity  of  a  single 
substation  will  be  large  enough  to  utilize  machinery  in  units  that 
may  be  operated  at  or  near  maximum  efficiency.  In  other  words, 
just  enough  units  may  be  in  service  at  any  one  time  that  the  load 
on  each  machine  is  very  near  its  full-load  rating.1  In  roads  of 
this  type  the  load  is  naturally  concentrated  at  a  few  points. 
Practically  all  lines  in  this  class  are  city  systems,  or  congested 
parts  of  trunk  lines  such  as  terminals  and  yards.  The  substa- 
tions may  therefore  be  placed  at  the  normal  centers  of  load. 
In  case  there  is  a  question  of  the  exact  location,  it  may  be  deter- 
mined by  assuming  the  average  load  at  the  mean  distance  on  each 
radial  line  fed  from  the  station,  and  finding  the  electrical  center 
of  gravity  of  the  total  load. 

Location  of  City  Substations. — The  location  of  substations  for 
city  lines  is  affected  to  a  large  extent  by  the  high  cost  of  land  at  the 
normal  centers  of  load.  For  this  reason  the  largest  roads  have 
found  it  economical  to  concentrate  as  much  capacity  in  a  single 
station  as  possible  without  excessive  drop  on  any  of  the  outlying 
lines.  This  concentration  has  been  carried  to  such  a  point 
that  synchronous  converters  of  extremely  large  rating  have  been 
built;  and  in  some  cases  converters  of  such  sizes  as  4000  kw. 
have  been  constructed  to  replace  units  of  1500  kw.,  the  better 
knowledge  of  design  enabling  manufacturers  to  produce  machines 
of  the  larger  size  which  can  actually  replace  the  smaller  units  on 
the  same  foundations.2 

Location  of  Substations  for  Interurban  Roads. — Interurban 
roads  fall  into  the  class  of  linear  distribution,  and  generally  can 
be  treated  in  a  much  simpler  manner  than  city  lines.  The  varia- 
tion in  the  number  of  substations  carries  with  it  a  considerable 
difference  in  the  cost  of  equipment,  as  well  as  in  that  of  operation. 
The  total  capacity  of  all  the  substations  must  be  equal  to  that  of 

1  The  effect  of  the  proper  operation  of  the  individual  units  on  the  all-day 
efficiency  of  the  substation  is  shown  in  a  paper  by  L.  P.  CRECELIUS,  Electric 
Journal,  October,  1914,  Vol.  XI,  p.  543. 

2  "History  of  the    Rotary  Converter    in    America,"  F.   D.   NEWBURY, 
Electric  Journal,  January,  1915,  Vol.  XII,  p.  27. 


320  THE  ELECTRIC  RAILWAY 

the  generating  station,  augmented  by  whatever  reserve  equipment 
is  required  due  to  uneven  distribution  of  the  load.  As  the  num- 
ber of  substations  is  increased,  the  number  and  total  capacity  of 
such  reserve  units  will  become  greater.  Conversely,  as  the  num- 
ber of  stations  is  decreased,  the  size  of  each  unit  which  can  be  eco- 
nomically employed  will  be  greater,  resulting  in  less  cost  of  equip- 
ment. The  cost  of  ground  and  building  will  not  vary  much 
with  the  capacity  of  the  station,  nor  will  the  attendance;  so  that  a 
very  decided  gain  can  be  made  from  greater  spacing.  The  cost 
of  attendance  will  also  be  very  nearly  constant,  no  matter  what 
the  capacity. 

Generally,  the  fixed  charges  representing  the  investment  in 
land,  buildings  and  equipment,  and  the  cost  of  operation,  will 
increase  as  a  function  of  the  number  of  substations;  while  the 
fixed  charges  on  the  secondary  copper,  and  the  value  of  the  loss 
in  the  distribution  circuit,  vary  inversely  with  it.  It  should, 
therefore,  be  possible  to  find  a  condition  where  the  total  cost  will 
be  a  minimum,  corresponding  to  a  definite  spacing. 

Two  methods  of  determining  the  proper  spacing  of  substations 
have  been  suggested:  the  first,  calculation  of  the  distance  by 
trial  for  any  particular  case,1  and  the  second,  by  an  analysis  of  the 
variables,  with  a  mathematical  solution.2  It  is  the  opinion  of 
engineers  that  the  exact  location  of  substations  cannot  be  made 
entirely  by  mathematical  treatment,  since  the  variables  which 
may  enter  will  vitiate  the  results  to  a  considerable  extent.  For 
instance,  on  interurban  roads  using  direct  current,  it  is  necessary 
to  have  an  attendant  at  the  substation  at  all  times.  His  duties 
will  not  occupy  the  entire  day,  so  that  it  is  usual  to  place  the  sub- 
stations so  far  as  possible  in  towns  located  along  the  line.  The 
operator  may  then  also  perform  the  duties  of  freight-  and  ticket- 
agent,  thus  calling  for  a  smaller  number  of  employees,  or  giving 
better  service,  than  would  otherwise  be  possible.  This  practice 
is  nearly  universal  with  interurban  roads. 

Effect  of  Potential  on  Substation  Spacing. — Since  the  loss  in  the 
distributing  circuit  varies  as  the  square  of  the  pressure,  it  is 
evident  that  the  most  economical  potential  is  the  highest  which 

1  "Some  Considerations  Determining  the  Location  of  Electric  Railway 
Substations,"  C.  W.  RICKER,  Transactions  A.  I.  E.  E.,  Vol.  XXIV  (1905), 
p.  1097. 

2  "The  Determination  of  the  Economic  Location  of  Substations  in  Elec- 
tric Railways,"  GERARD  B.  WERNER,  Transactions  A.  I.  E.  E.,  Vol.  XXVII; 
(1908),  p.  1201. 


SUBSTATIONS  FOR  ELECTRIC  RAILWAYS      321 

can  be  practically  employed.  As  has  been  stated  in  previous 
chapters,  direct-current  motors  have  been  standardized  for  600 
volts  and  multiples  of  this  value.  If  the  pressure  is  increased 
from  600  volts  to  1200  volts  on  the  contact  line,  the  losses  in 
the  distribution  circuit,  for  the  same  amount  of  copper,  will  be 
but  one-fourth  what  they  are  at  the  lower  potential.  On  the 
other  hand,  with  the  same  loss,  the  conductor  will  have  but  one- 
fourth  the  section  and  hence  cost  but  one-fourth  as  much.  There 
is  another  important  advantage  which  can  be  obtained  by  the  use 
of  higher  potentials.  The  economical  distance  between  sub- 
stations can  be  considerably  greater  with  the  same  total  operating 
cost.  This  will  result  in  practically  doubling  the  distance  be- 
tween stations.  It  also  has  the  effect  of  increasing  the  capacity 
of  each  substation,  so  that  the  investment  in  reserve  equipment 
can  be  less  and  the  operating  efficiency  higher. 

The  excellent  results  of  the  increase  of  potential  on  the  effi- 
ciency of  the  distribution  system  have  led  many  interurban  roads 
to  adopt  higher  working  pressures  than  the  old  standard  of  600 
volts.  It  has  already  been  mentioned  that  the  connection  of  two 
600-volt  motors  in  series  permits  operation  on  a  1200-volt  system, 
the  only  difference  being  that  the  motors  must  be  insulated 
for  a  higher  pressure,  and  the  control  equipment  must  be  changed 
accordingly.  The  advance  in  the  manufacture  of  railway  appa- 
ratus has  made  feasible  the  construction  of  motors  using  1200  volts 
on  a  single  commutator,  and  two  such  machines  may  be  placed 
in  series  on  a  2400-volt  circuit.  In  one  proposed  installation,  the 
pressure  per  commutator  is  to  be  increased  to  1500  volts,  making 
a  distribution  potential  of  3000  volts.  No  definite  limit  is  in 
sight  for  direct  current.  If  the  mercury  vapor  converter  fulfils 
expectations,  the  limiting  feature  will  be  the  commutating 
capacity  of  direct-current  motors. 

Alternating-Current  Distribution. — The  advantage  of  high 
trolley  potential  is  the  one  main  feature  which  has  led  to  the 
alternating-current  system.  In  this  case  there  is  no  limit  to  the 
distributing  e.m.f.,  since  stationary  transformers  along  the  track 
and  on  the  cars  and  locomotives  furnish  a  simple  means  of  obtain- 
ing any  pressure  suitable  for  the  apparatus  and  the  transmission. 
Single-phase  motors  of  the  commutator  type  are  all  inherently 
low-potential  machines;  but  the  use  of  a  transformer  makes  prac- 
tical any  pressure  on  the  distributing  circuit,  so  long  as  the  insu- 
lation can  be  taken  care  of. 

21 


322 


THE  ELECTRIC  RAILWAY 


The  use  of  stationary  transformers  removes  nearly  all  the  limi- 
tations from  the  operating  economy  of  the  converting  apparatus, 
since  the  demand  for  attendance  is  reduced  to  a  minimum. 
There  is  no  need  for  elaborate  controlling  devices,  as  with  the  syn- 
chronous converter  installations,  and  the  no-load  losses  are  so 
small  that  the  equipment  can  be  permanently  connected  for  the 
maximum  output.  The  greater  potential  possible  makes  con- 
centration of  the  substation  equipment  feasible,  giving  higher  load 
factors. 

Portable  Substations. — It  is  not  possible  to  predetermine  the 
load  on  a  railway  system  under  all  conditions.  The  growth  of 
traffic  may  be  different  from  what  was  expected  in  the  estimates, 
or  there  may  be  additional  service  required  for  portions  of  the  year. 


High  Tension 
Lead    '' 


Choke  Coif 


Negative  and 
Equalizer 
Ter 


FIG.  182. — Portable  substation. 

As  shown,  an  outdoor  type  transformer  is  used  for  lowering  from  the  transmission  line 
potential.     In  some  designs,  a  transformer  of  the  ordinary  indoor  type  is  used  instead. 

In  such  cases  it  is  not  desirable  to  permanently  install  sufficient 
substation  equipment  to  meet  the  maximum  demand,  since  it 
will  be  needed  for  but  a  few  months  in  the  year.  On  the  other  hand, 
operation  with  too  small  substation  capacity  is  unsatisfactory,  due 
to  the  large  drop  in  potential,  to  say  nothing  of  the  excessive  loss. 
In  recent  years,  many  interurban  roads  have  adopted  the  method 
of  using  portable  substations,  which  may  be  moved  from  point  to 
point  as  needed.  While  developed  for  the  purposes  mentioned, 
the  portable  substation  is  useful  when  building  a  new  line  or  an 
extension,  in  which  case  the  transmission  line  may  be  installed, 
the  permanent  converting  equipment  being  left  until  the  required 
capacity  and  the  correct  location  have  been  determined.  It  is 
also  useful  when  repairs  have  to  be  made  on  an  existing  station, 
for  the  portable  substation  can  be  placed  on  a  siding  near  the 


SUBSTATIONS  FOR  ELECTRIC  RAILWAYS      323 

permanent  one,  which  may  be  entirely  disconnected  while  repairs 
are  being  made. 

For  direct-current  roads,  the  converting  equipment  will  consist 
of  a  rotary  converter  of  proper  size,  with  suitable  transformers  and 
controlling  devices.  Such  a  station  is  shown  diagrammatically 
in  Fig.  182.  The  apparatus  is  placed  on  a  specially  designed  car, 
the  transformers  being  of  the  indoor  or  the  outdoor  type,  as 
desired.  No  motive  power  equipment  is  used,  the  car  being 
hauled  by  locomotives  from  point  to  point.  Converter  sub- 
stations of  this  type  are  usually  of  300  kw.  capacity,  although 
sometimes  larger. 

For  alternating-current  roads,  all  that  is  required  is  a  trans- 
former of  the  proper  characteristics.  This  can  usually  be  carried 
on  a  car  and  left  at  the  proper  location  to  aid  or  replace  the  per- 
manent equipment.  No  special  car  is  required  in  this  case. 


CHAPTER  XIV 
THE  TRANSMISSION  CIRCUIT 

Development. — In  the  preceding  chapters  the  characteristics 
of  the  distributing  circuit  have  been  considered  largely  apart  from 
any  connection  with  the  transmission  system.  It  is  evident  that 
the  successful  operation  of  an  electric  railway  does  not  depend  on 
the  use  of  high-tension  transmission  with  conversion  to  the  proper 
kind  of  current  for  motor  service;  but  the  latter  as  generated 
may  be  entirely  satisfactory,  provided  the  amount  of  power  to  be 
delivered  by  one  generating  station  is  sufficient  to  warrant  its 
operation  at  the  potential  of  the  distributing  circuit.  In  most 
cases  the  amount  of  power  which  can  be  so  concentrated  is  not 
enough  to  justify  such  an  arrangement.  The  reason  for  this  is 
entirely  because  of  the  economies  which  can  be  effected  by  the  use 
of  large  generating  systems. 

Improvements  in  power-plant  equipment,  coupled  with  large 
increase  in  the  commercial  capacities  of  the  units,  are  modifying 
conditions  so  that  a  system  correctly  laid  out  in  the  past  with 
individual  generating  stations  may  now  be  considered  inefficient 
beside  a  modern  one  with  the  power  supply  concentrated  in  a 
single  plant.  In  fact,  several  large  railroads  have  found  it 
economical  to  abandon  the  older  individual  power  stations, 
replacing  them  with  single  large  plants  and  high-tension  trans- 
mission with  low-tension  secondary  distribution.  The  advan- 
tages of  large  generating  units  will  be  considered  in  the  next 
chapter;  for  the  present  let  it  be  assumed  that  such  an  arrange- 
ment is  the  most  satisfactory  for  the  ordinary  railroad.  It  then 
becomes  necessary  to  transmit  the  power  so  produced  to  the  point 
where  it  is  to  be  utilized  with  a  minimum  of  loss;  or,  more 
strictly,  in  such  a  manner  that  the  total  cost  of  transmitting  the 
energy  will  be  least. 

Types  of  Transmission  Circuits. — As  already  shown,  electric 
energy  can  be  transmitted  either  by  direct  current  or  alternating 
current.  The  former  is  in  many  ways  superior,  since  but  a  single 
pair  of  conductors  is  required,  and  the  motors  which  can  be  used 

324 


THE  TRANSMISSION  CIRCUIT  325 

on  direct-current  circuits  are  in  some  respects  superior  to  alter- 
nating-current motors.  Certain  effects  of  the  alternating  cur- 
rent, such  as  inductance  and  capacity,  which  are  present  to  a 
considerable  extent  in  transmission  lines,  disappear  with  direct 
current.  But  the  latter  has  one  insurmountable  disadvantage: 
up  to  the  present  time  it  is  impossible  to  convert  it  from  one 
potential  to  another  without  the  use  of  rotating  machinery;  while, 
on  the  other  hand,  the  transformer  provides  a  simple  and  efficient 
means  for  doing  this  with  alternating  current.  It  is  this  one 
thing  which  has  generally  prohibited  the  use  of  direct  current  for 
long-distance  transmission. 

The  only  way  in  which  direct  current  has  been  used  for  trans- 
mission is  by  the  so-called  "Thury"  system,  in  which  a  constant 
current  is  employed  at  variable  potential.  This  has  already  been 
referred  to  in  the  previous  chapter.  It  requires  the  use  of  special 
rotating  machinery  at  each  end  of  the  transmission  line,  and  does 
not  possess  the  flexibility  of  the  constant  potential  system,  so 
that  its  application  has  been  exceedingly  limited. 

Alternating  current  is  available  at  a  number  of  commercial 
frequencies,  and  either  single-phase  or  polyphase.  It  is  shown  in 
all  text-books  on  electric  transmission  that  the  single-phase  and 
two-phase  circuits  require  a  greater  weight  of  conductor  than  the 
other  polyphase  systems;  so  that,  unless  there  is  some  other  com- 
pensating advantage,  the  first-mentioned  forms  of  electric  power 
are  inferior  to  the  others.  The  single-phase  requires  the  simplest 
machinery,  and  only  two  wires  are  necessary  for  the  electric  cir- 
cuits. It  has  the  disadvantage  of  more  expensive  generating 
equipment;  and  the  motors  for  operation  on  a  single  phase  are  not 
so  satisfactory  for  general  purposes  as  polyphase  motors.  Even 
when  a  single-phase  contact  line  is  to  be  employed,  there  are 
enough  advantages  in  polyphase  transmission  that  it  is  sometimes 
used  in  that  connection. 

When  the  distributing  circuit  is  to  be  arranged  for  direct 
current,  the  use  of  polyphase  transmission  is  universal,  partly 
on  account  of  the  saving  in  cost  of  conductor  and  partly  because 
of  the  superiority  of  the  machinery.  So  far  as  transmission  econ- 
omy goes,  the  two-phase  and  the  single-phase  are  on  a  par;  but 
even  though  the  latter  requires  four1  wires  against  two  for  the 
former,  it  is  preferable  on  account  of  the  better  operation  of  the 

1  Three-wire  two-phase  circuits  are  practically  never  used  for  trans- 
mission purposes,  on  account  of  the  lack  of  symmetry. 


326  THE  ELECTRIC  RAILWAY 

equipment.  The  three-phase  circuit,  for  the  same  transmission 
loss,  requires  but  three-fourths  as  much  conductor  material  as 
either  the  single-phase  or  the  two-phase;  and  the  machinery  is  at 
least  as  good  as,  and  as  cheap  as,  two-phase  apparatus.  For  this 
reason  the  two-phase  circuit  has  become  practically  obsolete  for 
all  kinds  of  electric  transmission  and  distribution. 

The  arguments  in  favor  of  the  three-phase  circuit  apply  with 
equal  force  to  higher  numbers  of  phases;  but  these  require  addi- 
tional wires  without  a  corresponding  gain  in  efficiency.  It  is 
true  that  a  larger  number  increases  the  capacity  of  rotating  ma- 
chinery; but  these  advantages  can  be  obtained  with  three-phase 
transmission  by  a  simple  arrangement  of  the  raising  and  lowering 
transformers.  For  these  reasons  the  higher  polyphase  circuits 
have  never  been  used  commercially  for  this  purpose;  and  today, 
three-phase  is  universally  adopted  whenever  transmission  with 
polyphase  circuits  is  desired. 

Need  for  High  Tension. — It  has  been  shown  that  the  loss  in  the 
electric  circuit,  for  a  given  size  of  conductor  and  amount  of  power 
transmitted,  varies  inversely  as  the  square  of  the  potential.  It 
is  for  this  reason,  and  for  this  reason  alone,  that  the  use  of  high 
potential  is  needed  for  the  economical  transmission  of  power. 
This  relation  holds  true,  irrespective  of  the  kind  of  current,  phase 
or  frequency.  If  there  were  no  limitations,  there  would  be  no 
inherent  objections  to  the  use  of  extremely  high  potentials  for  all 
kinds  of  power  transmission.  Practically,  the  use  of  high-tension 
circuits  brings  a  number  of  disadvantages  which  must  be  over- 
come to  make  them  practical. 

The  most  troublesome  feature  to  be  taken  into  account  in  the 
use  of  high  tension  is  the  requirement  of  properly  insulating  the 
conductors,  both  from  each  other  and  from  the  earth.  The 
trouble  from  this  cause  is  small  at  low  pressures,  but  when  the 
potential  exceeds  rather  definite  limits,  the  difficulties  increase 
very  rapidly.  In  addition  to  this,  the  effects  of  capacitance  in- 
crease with  the  potential,  so  that  special  precautions  must  be 
taken  to  avoid  difficulty  from  this  source.  Lightning  also  re- 
quires particular  attention.  It  is  interesting  to  note  that  when 
extremely  high  pressure  lines  are  operated,  the  need  for  protec- 
tion against  surges  due  to  short  circuits  or  sudden  opening  of  the 
switches  exceeds  that  against  lightning.  In  such  cases  lightning 
has  been  found  to  cause  little  or  no  disturbance  on  the  line,  and 
sometimes  does  not  even  interfere  with  the  continuity  of 
operation. 


THE  TRANSMISSION  CIRCUIT  327 

Choice  of  Potential. — The  proper  potential  for  the  transmission 
circuit,  as  well  as  the  size  of  conductor  to  be  used,  can  be  deter- 
mined with  some  exactness  by  the  application  of  well-known  en- 
gineering principles.  That  potential  should  be  used  which  will 
give  the  lowest  total  annual  cost  for  wasted  energy  and  interest 
and  depreciation  "on  the  investment.  This  may  be  found  by 
Kelvin's  law,  as  in  the  case  of  the  distributing  circuit. 

Other  considerations  often  affect  the  result  in  the  determination 
of  the  potential  and  size  of  conductor,  so  that  the  best  values, 
as  found  theoretically,  may  not  be  the  ones  finally  adopted.  The 
use  of  standard  equipment  will  generally  dictate  that  the  pressure 
adopted  be  one  of  a  comparatively  few  for  which  apparatus  is 
made  commercially.  This  may  effect  a  considerable  reduction  in 
first  cost,  which  will  overbalance  possible  saving  in  energy  due  to 
a  higher  potential.  Again,  many  electric  roads  are  now  becoming 
interconnected  through  high-tension  networks,  and  it  may  be 
better  to  use  the  existing  potential  of  the  network  rather  than  to 
connect  through  transformers. 

In  certain  cases  the  size  of  conductor,  as  determined  for 
economy,  may  be  less  than  that  which  can  be  used  commercially 
on  a  long  line.  If  no  saving  in  cost  of  conductor  is  to  be  effected, 
there  is  no  advantage  in  the  use  of  an  extremely  high  potential, 
since  the  difficulties  in  transmission  increase  with  the  pressure. 
The  required  regulation  of  the  circuit  may  dictate  a  wire  in  ex- 
cess of  the  most  economical  size. 

A  great  many  interurban  roads  in  the  Middle  West  have 
practically  standardized  on  potentials  of  16,500  and  33,000  volts 
for  transmission  systems.  While  these  pressures  are  not  high, 
according  to  modern  standards,  the  amounts  of  power  to  be  trans- 
mitted are  not  so  large  as  to  occasion  excessive  loss.  As  the 
size  of  the  road  increases,  the  need  for  higher  potentials  is  more 
keenly  felt,  and  a  readjustment  of  the  circuits  may  become 
necessary  for  the  highest  economy. 

When  purchasing  transforming  equipment,  it  is  often  possible 
to  anticipate  future  changes  in  operating  potential  by  having  the 
transformers  wound  for  a  higher  pressure  than  that  on  which  they 
are  used.  This  may  be  done  by  bringing  out  taps  from  inter- 
mediate points  on  the  windings,  by  connecting  the  high-tension 
coils  in  parallel,  or  by  arranging  the  primaries  in  delta.  If  it  is 
desired  to  increase  the  transmission  pressure,  the  transformers 
will  then  be  ready  for  the  change  with  no  added  cost  save  the 
work  of  rearranging  the  connections. 


328  THE  ELECTRIC  RAILWAY 

Regulation  of  the  Transmission  Line. — In  all  constant  poten- 
tial electric  circuits,  it  is  essential  that  the  variation  in  pressure 
shall  not  exceed  a  certain  amount,  depending  on  the  character 
of  the  apparatus  connected  to  it.  While  the  operation  of  electric 
cars  and  locomotives  does  not  demand  a  very  close  regulation  in 
the  distributing  circuit,  the  operation  of  the  substation  equipment 
and  of  the  generators  is  affected  injuriously  by  wide  fluctuations 
in  the  transmission  pressure.  In  addition  to  this,  the  power 
factor  of  the  alternating-current  circuit  has  a  marked  effect  on 
the  performance  and  on  the  line  drop. 

Some  form  of  automatic  regulation  is  very  desirable  to  keep  the 
potential  of  the  transmission  circuit  at  a  nearly  constant  value. 
This  may  be  obtained  in  direct-current  circuits  by  compounding 
the  generators,  so  that  the  e.m.f.  produced  will  increase  enough 
with  load  to  compensate  for  the  line  drop.  When  alternating 
current  is  used,  this  method  of  regulation  has  never  met  with 
success,  for  it  requires  complication  of  the  machines  and  does 
not  give  entirely  satisfactory  operation.  When  synchronous 
machinery,  such  as  rotary  converters,  is  used  at  the  receiving 
end  of  the  line,  regulation  may  be  effected  by  over-excitation, 
and  drawing  the  current  through  reactance.  This  combination 
will  cause  the  leading  current  taken  on  account  of  the  over- 
excitation  to  produce  a  negative  impedance  drop,  which  has  the 
effect  of  compounding  the  transmission  line.  Where  the  regula- 
tion must  be  closer  than  can  be  obtained  with  this  arrangement, 
or  where  it  is  desirable  to  keep  the  power  factor  constant,  auto- 
matic potential  regulators  can  be  used. 

Close  regulation  is  not  a  prime  essential,  so  far  as  the  successful 
operation  of  most  types  of  railway  motors  is  concerned.  We 
have  seen  that  the  allowable  drop  is  quite  considerable,  especially 
for  interurban  operation.  But  in  general  poor  regulation  usually 
carries  with  it  low  efficiency,  so  that  the  pressure  should  not  be 
allowed  to  vary  through  such  wide  limits  in  the  transmission  line 
as  in  the  distribution  circuit.  The  total  permissible  drop  must 
be  divided  between  the  different  parts  of  the  system,  unless  some 
form  of  automatic  pressure  control  is  employed.  If  synchronous 
converters  are  used  without  any  form  of  regulator,  the  variation 
in  potential  is  transmitted  through  the  machines  and  the  trans- 
formers directly,  so  that  the  drop  in  the  transmission  line  will 
add  to  that  in  the  distributing  circuit.  When  an  automatic 
regulator  is  employed,  the  drop  in  the  two  circuits  can  be  made 
practically  independent. 


THE  TRANSMISSION  CIRCUIT  329 

Mechanical  Arrangements  of  Transmission  Lines. — In  many 
cases,  the  transmission  line  for  an  electric  railway  differs  ^from 
that  for  general  power  purposes,  mainly  because  the  wire  circuit 
can  be  placed  on  the  same  poles  that  carry  the  distributing  feeders 
and  furnish  the  support  for  the  contact  conductor.  This  cheap- 
ens the  construction  materially  over  that  used  for  a  separate  line, 
since  the  only  expense  incurred  above  that  for  the  transmission 
wire,  insulators  and  cross-arms  is  due  to  the  extra  length  of  poles 
required  for  supporting  the  high-tension  circuit.  On  account  of 
this,  it  may  in  certain  cases  be  cheaper  to  use  a  fairly  low  tension, 
rather  than  to  adopt  a  type  of  insulator  which  will  require  a 
separate  pole  line  for  the  transmission  system. 

These  remarks,  of  course,  do  not  apply  to  roads  operating  with 
the  third  rail,  where  any  pole  lines  which  may  be  erected  are  en- 
tirely for  the  transmission  and  the  distribution  circuits;  nor  where 
conditions  are  such  that  it  is  necessary  to  use  underground  con- 
ductors. In  cities,  the  transmission  line  can  ordinarily  be  made 
much  more  direct  than  to  follow  the  railway  track. 

The  high-tension  circuit  is  usually  run  with  copper  wires  of  the 
proper  size,  but  occasionally  aluminum  is  employed  instead. 
The  relative  merits  of  the  two  metals  have  been  the  subject  of 
considerable  discussion,  and  the  final  decision  usually  lies  with 
the  metal  which  is  cheaper  at  the  time  of  purchase.  The  fluctua- 
tions of  the  metal  market  are  so  rapid  and  so  erratic  that  it  is  not 
possible  to  state  definitely  that  the  advantage  lies  with  either. 

In  some  cases  a  single  transmission  circuit  is  used  alone;  but 
in  others,  to  avoid  interruption  of  service,  two  or  more  are  em- 
ployed in  parallel,  either  on  the  same  pole  line  or  on  entirely  sepa- 
rate structures.  The  choice  depends  largely  on  the  conditions  of 
operation.  In  climates  where  there  are  few  periods  of  severe 
weather,  the  advantage  of  duplicate  lines  is  much  less  than  where 
storms  are  frequent  and  violent.  This  is  a  question  which  must 
be  settled  independently  for  each  separate  case. 

The  determination  of  mechanical  stress  in  transmission  lines 
can  be  accomplished  by  the  same  method  as  that  given  for  the  dis- 
tribution circuit.  Added  load  due  to  ice  is  of  greater  importance 
in  this  case,  on  account  of  the  smaller  size  of  conductor  ordinarily 
used,  and  the  longer  spans  which  are  often  employed.  The  side 
strain  caused  by  wind  is  also  of  considerable  moment,  especially 
when  aluminum  conductors  are  used. 


CHAPTER  XV 
POWER  GENERATION 

Requirements. — The  requirements  of  electric  railways  are  in 
no  material  way  different  from  those  for  other  users  of  electric 
power.  The  load,  it  is  true,  is  subject  to  wide  fluctuations,  but 
this  can  equally  well  be  said  of  other  consumers.  There  is,  there- 
fore, no  inherent  reason  why  the  power  plants  for  railway  service 
should  differ  in  any  great  respect  from  those  for  general  power 
purposes. 

Capacity  of  the  Power  Station. — After  the  capacities  of  the 
different  substations  have  been  determined,  as  indicated  in  pre- 
vious chapters,  similar  calculations  for  the  power  plant  are 
comparatively  easy.  The  all-day  load  charts  for  the  various 
substations  should  be  superposed  to  give  the  total  demand  on  the 
power  plant.  This  is  a  process  of  summation,  the  instantaneous 
loads  being  added  directly  together.  From  the  load  chart  for 
the  power  station,  obtained  in  this  manner,  the  total  output  may 
be  found  by  integration,  and  the  average  load  determined  by  di- 
viding the  energy  output  by  the  time  used  in  the  integration. 

The  size  of  individual  units  depends  on  the  average  load,  and 
also  on  the  momentary  overload.  Their  number  should  be  so 
chosen  that,  at  any  period  of  the  day  (except,  perhaps,  when  the 
load  is  the  very  lightest),  the  machines  in  service  will  be  work- 
ing at  or  near  full  load.  This  consideration  is  important  if  the 
highest  efficiency  is  to  be  reached  in  operation  of  the  plant.  In 
the  smallest  stations,  where  only  two  or  three  machines  will  be 
used,  it  is  not  possible  to  do  more  than  approximate  this  con- 
dition; but  in  the  larger  systems,  the  number  of  units  can  be 
chosen  with  regard  to  economy  in  operation. 

The  efficiency  of  most  electric  generators  is  greatest  at  full  load, 
or  at  an  output  slightly  less  than  this  point,  although  the  varia- 
tion in  efficiency  from  half  load  to  load-and-a-quarter  is,  in  mod- 
ern machines,  quite  small.  Outside  these  limits,  the  efficiency 
falls  off  quite  rapidly;  and  if  generators  are  to  be  operated  at  light 
load  for  large  portions  of  the  day,  the  efficiency  of  the  station  may 

330 


POWER  GENERATION  331 

be  reduced  materially.  Proper  choice  of  units  will,  therefore, 
be  ineffective  unless  accompanied  by  correct  operation. 

A  lower  limit  to  the  subdivision  of  the  generators  also  exists. 
The  cost  of  electrical  machinery  increases  per  kilowatt  as  the 
size  of  unit  is  decreased,  and  the  maximum  operating  efficiency 
becomes  lower.  It  is  important  that  the  units  be  as  large  as  is 
consistent  with  proper  subdivision  of  the  load,  that  these  advan- 
tages in  cost  and  efficiency  of  the  larger  machines  may  be  availed 
of.  In  any  particular  case,  the  proper  selection  of  apparatus 
should  be  carefully  considered.  The  possibility  of  future  ex- 
tensions to  the  system  should  not  be  overlooked,  for  this  may 
influence  to  a  considerable  degree  the  selection  of  generating 
equipment. 

Power  Plant  Location. — Abstractly  considered,  the  location 
of  the  power  plant  may  be  determined  in  the  same  way  as  that  of 
the  substations.  The  center  of  load  can  be  found,  and  the  station 
may  be  built  at  this  point.  In  general,  such  a  situation  will 
be  at  a  place  where  it  is  impractical  to  build  a  power  plant.  For 
a  successful  steam  plant,  the  location  must  be  such  that  coal  can 
be  delivered  cheaply  and  easily,  and  an  adequate  supply  of  water 
for  the  boilers  and  condensers  must  be  available.  The  first  con- 
sideration practically  dictates  that  the  station  shall  be  situated  on 
the  line  of  a  steam  railroad,  unless  a  suitable  interchange  agree- 
ment can  be  made  for  operating  coal  trains  over  the  tracks  of  the 
electric  road.  Sometimes  it  is  feasible  to  place  the  power  plant 
on  the  bank  of  a  navigable  stream,  in  which  case  coal  can  often 
be  delivered  by  water  at  a  cost  less  than  possible  when  rail  de- 
livery is  used.  The  second  consideration  generally  demands  that 
the  station  be  located  on  or  near  a  river  or  creek  of  sufficient  size 
for  the  water  supply.  In  certain  cases  it  may  be  cheaper  to 
pipe  water  considerable  distances;  as,  for  example,  to  use  a  city 
water  supply,  and  have  some  form  of  water  cooling  plant  in  con- 
nection with  the  condensing  system.  Local  conditions  affect 
these  points  so  much  that  it  is  not  possible  to  formulate  any  gen- 
eral rules  for  location. 

The  most  important  single  thing  which  will  affect  the  position 
of  the  plant,  after  these  primary  considerations,  is  the  cost  of 
land.  This  will  practically  prohibit  the  erection  of  a  station  in 
the  center  of  a  city,  which  would  be,  for  example,  the  ideal  place 
for  it  in  connection  with  a  street  railway.  It  is  frequently  far 
cheaper  in  total  operating  cost  to  locate  the  station  outside  the 


332  THE  ELECTRIC  RAILWAY 

city  where  land  is  cheap,  and  where  the  advantages  of  coal  and 
water  supply  may  be  better  than  in  the  more  central  position. 

When  power  is  to  be  transmitted  to  substations  at  high  poten- 
tial, the  exact  location  of  the  plant  has  but  a  small  effect  on  the 
total  economy  of  the  system.  In  such  cases  there  is  no  great  ad- 
vantage in  putting  the  station  at  the  center  of  load,  and  it  may  be 
preferable  to  have  it  at  a  point  far  removed  from  the  ideal  posi- 
tion, if  the  other  factors  can  be  better  met. 

Hydraulic  Power. — Where  water  power  is  available,  it  is  always 
desirable  to  consider  using  this  in  place  of  steam.  In  order  to 
compete  with  steam  power,  the  total  cost  of  generation  with  water 
power  must  be  as  small  as,  or  smaller  than,  that  for  steam. 
The  operating  costs  for  hydro-electric  plants  are  usually  materially 
lower  than  those  for  steam  stations;  but  the  construction  costs  are 
so  much  higher  that  there  is  often  little  difference  between  the 
total  annual  expenses. 

When  hydraulic  power  is  used,  the  location  of  the  plant  is,  of 
course,  the  outcome  of  natural  conditions,  and  cannot  be  changed 
materially.  In  cases  where  the  hydro-electric  development  must 
be  placed  a  long  distance  from  the  railroad  system,  the  question 
may  arise  whether  it  would  be  cheaper  to  build  a  steam  power 
plant  nearer  the  center  of  load,  thus  doing  away  with  a  long 
transmission  line.  Such  problems  must  be  considered  individu- 
ally on  their  merits. 

Choice  of  Equipment. — In  the  selection  of  power  station  ma- 
chinery, there  are  many  different  types  which  may  be  used,  and 
considerable  engineering  judgment  is  necessary  to  get  the  best 
combination  for  a  particular  installation.  Aside  from  those  for 
hydraulic  power,  the  prime  movers  available  are  steam  turbines, 
reciprocating  steam  engines,  and  internal  combustion  engines. 
The  choice  between  them  depends  to  a  considerable  extent  on  the 
size  of  the  plant  and  the  cost  of  fuel.  With  large  units  and  fairly 
low  prices  for  coal,  the  steam  turbine  is  the  most  economical  prime 
mover  available.  With  smaller  machines,  the  reciproctaing 
engine  is  not  at  such  a  great  disadvantage.  The  field  of  the  gas 
engine  is  rather  uncertain,  and  it  does  not  appear  to  be  a  serious 
competitor  of  steam  for  large  sizes. 

Power  Plant  Construction. — No  attempt  will  be  made  to  con- 
sider the  actual  design  of  power  plants.  For  such  information, 
reference  should  be  made  to  any  good  book  on  power  plant  design. 
It  should  be  noted  that  the  type  of  plant  will  be  influenced  to  some 


POWER  GENERATION  333 

extent  by  the  cost  of  land  available  for  the  station.  If  it  is  neces- 
sary to  build  in  the  congested  part  of  a  city,  where  land  is  ex- 
pensive, apparatus  should  be  used  which  is  of  the  greatest  com- 
pactness. This  consideration  usually  calls  for  the  steam  turbine 
in  preference  to  other  prime  movers.  In  some  cases  an  attempt 
has  been  made  to  still  further  reduce  the  ground  required  by 
placing  the  equipment  in  two  stories.  This  arrangement  has  not 
been  uniformly  successful. 

Purchased  Power. — A  movement  has  been  put  forward  by  the 
large  central  stations  within  the  last  few  years  to  advocate  the 
use  of  energy  purchased  from  power  companies  for  railroad  operal 
tion.  There  are  several  reasons  why  this  should  be  the  idea- 
arrangement,  and  why  the  cost  of  energy  to  the  railroad  should 
be  lower  when  purchased  than  when  generated  in  the  road's  own 
plant.  The  power  company  is  specifically  in  the  business 
of  producing  and  selling  energy.  The  entire  staff  has  been  trained 
to  that  end;  and  better  results  should  be  obtained  with  such  an 
organization  than  by  that  of  a  railroad,  whose  primary  business 
is  to  furnish  transportation.  Coal  and  supplies  should  be  bought 
at  lower  prices,  both  on  account  of  the  better  organization,  and 
on  account  of  the  larger  amounts  purchased. 

A  large  central  station  generates  such  great  amounts  of  energy 
that  the  railroad  load  is  but  a  small  portion  of  the  total.  It  is 
possible  to  use  more  efficient  prime  movers  and  electric  machinery 
than  are  available  for  the  railroad  alone.  The  larger  size  of  the 
units,  and  the  concentration  of  power  in  a  single  station,  reduces 
the  cost  of  producing  energy  by  a  not  inconsiderable  amount. 
But  the  greatest  argument  in  favor  of  this  method  of  operation  is 
the  " diversity  factor.'7  If  the  railroad  load  came  at  exactly  the 
same  time  as  the  general  demand,  there  would  be  no  advantage 
in  central  station  power,  other  than  those  mentioned.  Ex- 
perience shows,  however,  that  the  peaks  of  the  various  loads  never 
coincide.  For  example,  in  a  large  city  transportation  is  required 
in  greatest  amount  at  times  immediately  before  the  factories  and 
offices  open,  and  just  after  they  close.  Even  a  small  diversity  in 
time  may  make  a  great  difference  in  the  total  capacity  of  generating 
equipment  needed.  If  the  railway  peaks  could  be  made  to  come 
during  light  load  for  other  purposes,  it  might  easily  be  possible 
that  the  entire  railway  service  in  a  large  city  could  be  furnished 
by  a  central  power  plant  with  no  addition  to  the  equipment  re- 
quired for  other  users.  This  condition  cannot  be  attained,  for 


334  THE  ELECTRIC  RAILWAY 

some  railway  service  is  needed  at  the  peak  of  the  general  power 
load,  and  the  maximum  railway  load  coincides  very  nearly  with 
a  large  demand  for  power.  But  even  a  slight  difference  permits 
a  considerable  reduction  in  total  plant  capacity.  Electrified 
steam  roads  handling  large  amounts  of  freight  have  found  it 
possible  to  run  many  of  the  freight  trains  at  night,  when  the  gen- 
eral power  demand  is  a  minimum.  In  this  way  the  maximum 
railway  load  may  be  kept  entirely  away  from  the  industrial  and 
lighting  peaks,  so  that  the  best  possible  utilization  of  the  power 
plant  machinery  may  be  realized. 

It  is  this  diversity  feature  which  makes  it  feasible  for  the  power 
companies  to  make  such  attractive  prices  for  energy  to  railway 
companies.  On  the  side  of  the  railroad,  it  is  easy  to  see  that,  if 
power  can  be  purchased  for  what  its  generation  in  an  independent 
plant  would  cost,  and  no  investment  is  required,  it  forms  a  very 
good  way  of  solving  the  problem.  Even  a  large  trunk  line  may 
find  it  profitable  to  buy  power. 

As  an  example  of  what  can  be  done  with  purchased  power,  it 
may  be  stated  that  practically  all  energy  for  operation  of  the 
electric  roads  in  Chicago,  both  surface  and  elevated,  is  generated 
in  the  stations  of  the  Commonwealth  Edison  Company,  and  sold 
to  the  roads  at  a  price  so  low  that  they  have  found  it  advanta- 
geous to  shut  down  their  own  plants  completely.  Further  than 
this,  the  substations  are  being  operated  by  the  power  company, 
and  power  is  distributed  from  a  single  station  to  several  different 
roads.  In  this  way  the  load  factor  of  the  substations  is  improved, 
and  the  total  cost  of  equipment  decreased,  while  the  efficiency 
is  raised.  Equally  good  results  might  be  obtained  in  other  cities, 
both  for  the  city  roads,  and  for  interurban  lines  entering  them. 

In  this  connection,  it  is  only  fair  to  state  that  many  of  the 
smaller  central  stations  have  been  built  to  accommodate  both  the 
railway  load  and  the  lighting  load,  and  have  been  so  operated  for 
years.  The  older  plants,  especially  in  small  cities,  have  usually 
been  equipped  with  separate  units  for  the  railway  and  the  lighting 
and  industrial  loads.  The  development  of  potential  regulators 
has  changed  the  situation  so  that  there  is  no  reason  why  power 
for  railway  service  and  for  lighting  should  not  come  from  the 
same  machine.  In  fact,  the  use  of  larger  units  has  the  effect  of 
minimizing  the  bad  results  due  to  the  sudden  fluctuations  of  load 
which  are  incident  to  railway  operation,  while  not  affecting  to 
any  extent  the  control  of  potential  for  the  lighting  circuits. 


CHAPTER  XVI 
SIGNALS  FOR  ELECTRIC  ROADS 

Uses  of  Signals. — The  early  railroads  were  operated  without 
signals  of  any  sort.  This  was  possible  because  the  speeds  were 
low  and  the  trains  light.  When  higher  speeds  and  heavier  trains 
became  common,  it  was  found  necessary  to  introduce  devices  to 
prevent  attempts  to  use  the  same  track  for  more  than  one  train  at 
a  time.  This  became  more  and  more  necessary  as  traffic  in- 
creased, and  the  tracks  became  more  fully  occupied.  Expressed 
in  modern  terms,  the  primary  use  for  signals  is  to  obtain  "Safety 
First.'*  The  need  for  some  form  of  protection  to  prevent  acci- 
dents increases  rapidly  as  the  traffic  develops,  and  more  particu- 
larly as  higher  speeds  are  employed. 

Another  legitimate  reason  for  the  employment  of  signals  is  to 
promote,  through  intelligent  use  of  the  track,  a  greater  capacity 
than  is  otherwise  possible.  To  accommodate  the  maximum 
traffic,  trains  should  follow  one  another  as  rapidly  as  can  be  done 
with  safety,  and  speeds  should  be  as  high  as  practical  without 
requiring  too  great  spacing  between  them  to  permit  stopping  in 
case  the  track  is  found  to  be  occupied.  The  various  forms  of 
automatic  block  signals,  when  properly  applied,  will  increase  by  a 
considerable  amount  the  number  of  trains  which  can  be  run  over  a 
given  track,  and  at  the  same  time  make  the  operation  decidedly 
more  safe  than  when  other  forms  of  control  are  employed. 

Kinds  of  Signals. — A  number  of  devices,  which  are  often  over- 
looked in  modern  operation,  constitute  the  backbone  of  the  signal 
system  on  any  road.  It  is  well  to  know  which  of  these  are  avail- 
able, and  which  are  used,  since  they  form  a  valuable  adjunct  to 
the  better-known  types  of  signals  which  the  public  ordinarily 
considers. 

Signals  are  of  two  main  kinds :  audible  and  visible.  The  former 
usually  consist  of  the  bell,  the  whistle  and  the  torpedo.  These 
may  be  operated  by  the  engineer  of  the  train,  or  by  some  other 
member  of  the  train  crew,  or  in  certain  cases  by  members  of  the 
operating  force  not  directly  connected  with  the  train  service. 

335 


336  THE  ELECTRIC  RAILWAY 

The  use  of  these  devices  is  invaluable  in  many  critical  situations, 
and  must  not  by  any  means  be  overlooked.  Visible  signals  are 
of  two  types :  movable  and  fixed.  The  movable  signals  are  the 
trainman's  lantern  or  flag,  the  fusee,  and  other  devices  of  the  same 
general  character.  Their  use  is  largely  the  same  as  that  of  the 
audible  signals,  and  the  two  are  often  employed  in  conjunction. 

The  fixed  signals  are  those  which  are  placed  in  permanent  loca- 
tions ^along  the  track,  where  they  may  be  observed  by  the  engi- 
neers of  passing  trains.  The  simplest  of  them  have  one  aspect 
only,  and  the  indication  given  is  to  be  observed  invariably. 
Such  are  the  whistle  post,  drawbridge  signs,  and  slow  or  stop 
signs.  These  signals  have  the  effect  of  warning  the  engineman  of 
the  character  of  the  track  ahead,  or  to  remind  him  of  a  duty  he 
must  invariably  perform. 

Fixed  signals  having  more  than  one  aspect  are  often  employed  ; 
and  it  is  this  type  which  is  brought  before  the  public  most  often 
in  connection  with  train  operation.  In  this  class  fall  switch 
targets,  train  order  signals,  block  signals  and  interlocking  signals. 

Methods  of  Displaying  Indications. — In  the  use  of  signals  of 
any  sort,  a  great  deal  depends  on  the  methods  employed  for 
imparting  their  meaning  to  the  train  crew.  In  general,  the  indica- 
tion is  displayed  at  a  fixed  point  along  the  right-of-way,  whether 
for  a  train-order  system,  an  interlocking  signal  or  a  block  signal, 
and  regardless  of  whether  the  system  is  manual  or  automatic  in 
character. 

A  marked  variation  in  signal  indications  may  be  possible  when 
they  are  to  be  viewed  by  day;  but  for  night  operation,  colored 
lights  are  almost  invariably  employed.  The  difference  between 
the  night  signals  is  due  to  the  methods  for  changing  the  color  of 
light  displayed.  Where  electric  lamps  are  used,  the  most  general 
method  for  displaying  the  indication  is  to  have  a  number  of 
lamps  behind  colored  lenses,  the  controlling  circuits  being  so 
arranged  that  one  or  more  lamps  may  be  lighted  to  convey 
different  information.  With  oil  lamps,  the  signal  is  usually  given 
by  a  single  lamp,  the  change  in  color  being  accomplished  by  mov- 
ing a  sector  with  different  colored  glasses  in  front  of  the  light. 

For  daylight  indications,  the  oldest  and  most  widely  used  device 
is  the  semaphore.  This  consists  of  a  blade,  mounted  on  a  suitable 
support,  and  in  a  vertical  plane  perpendicular  to  the  track.  It  is 
rotatable  about  a  fixed  point  near  one  end,  and  the  indication  is 
given  by  its  position.  There  are  four  possible  arrangements  of 


SIGNALS  FOR  ELECTRIC  ROADS  337 

the  semaphore  blade,  depending  on  which  quadrant  is  used  for 
the  rotation.  The  maximum  rotation  used  is  never  more  than 
90°,  one  of  the  positions  being  horizontal.  The  American 
Electric  Railway  Engineering  Association  has  adopted  as  stand* 
ard  the  following  with  relation  to  the  use  of  semaphore  signals:1 

"Where  semaphore  signals  are  used  they  shall  be  so  ar- 
ranged as  to  indicate  three  positions  in  the  upper  left- 
hand  quadrant." 

It  is  rather  expensive  to  install  and  maintain  semaphore  sig- 
nals, so  that  electric  roads  have  been  trying  to  find  other  types 
of  indicators  which  will  be  satisfactory  at  a  lower  cost.  Within 
the  last  few  years,  great  progress  has  been  made  in  the  use  of 
lamps  for  daylight  signaling.  To  be  satisfactory  in  this  service, 
the  lamp  must  be  equipped  with  a  lens  which  will  properly  direct 
the  rays,  and  be  carefully  shaded  so  that  it  will  not  be  interfered 
with  by  direct  sunlight.  From  the  excellent  results  which  have 
been  obtained  with  lamp  signals,  it  seems  that  they  are  entirely 
adequate  for  day  use.  On  the  other  hand,  there  is  a  large 
advertising  value  in  any  kind  of  signal  system,  and  the  more 
prominent  the  indication,  the  greater  the  advertisement. 
Semaphores  are  without  question  more  readily  observed  by 
the  traveling  public,  and  their  indications  are  plainer  than 
those  of  any  other  form  of  signal  in  use;  so  that  from  this 
standpoint  they  have  received  more  favorable  attention  in 
comparison  to  other  forms. 

Colored  discs  have  been  used  to  a  small  extent  for  day  indica- 
tions, but  they  possess  no  advantage  over  the  semaphore  and, 
like  it,  require  colored  lights  at  night.  They  are  now  nearly 
obsolete  on  all  railroads. 

Signal  Indications. — A  signal  is  to  give  certain  information  to 
the  enginemen,  and  the  more  certain  it  is,  the  better  the  system. 
The  most  usual  indications  to  be  given  are  " stop "  and  " proceed." 
In  some  methods  of  signaling,  a  third  indication,  "  proceed  with 
caution,"  is  also  used.  The  standard  American  Electric  Railway 
Engineering  Association's  indications  are:  (a)  Stop,  (6)  Proceed 
with  caution,  (c)  Proceed. 

These  may  be  interpreted  in  somewhat  different  ways,  depend- 
ing on  the  type  of  signal  system  used.  The  "  stop  "  signal  usually 

1  Engineering  Manual,  American  Electric  Railway  Engineering  Association, 
Section  Ss  2a. 
22 


338 


THE  ELECTRIC  RAILWAY 


conveys  the  additional  information  that  there  is  a  train  directly 
ahead,  or  that  some  abnormal  condition  makes  it  essential  that 
the  train  should  not  proceed.  It  may  mean  merely  that  the 
train  crew  should  report  for  orders. 

The  " proceed  with  caution"  indicates  that,  while  it  is  not  safe 
to  go  ahead  at  full  speed,  it  is  possible  to  do  so  at  reduced  speed, 
prepared  to  stop  short  of  any  obstruction.  Where  the  signal 


Stop 


Stop  and 
Sfay 


Stop  and 
Proceed 


Red 


Proceed 

with 
Caution 


Proceed,  Next 
Signal  erf- 
Stop 


Proceed 

Under  Corrtrol 


felfow 


Yellow 


Yellow 


Proceed 


Green 


Green 


Lighted  Lamps  Shown    mite,  Colors  Indicated 
FIG.  183. — Aspects  in  three-position  signaling. 

These  indications  have  been  adopted  as  standard  by  the  American  Electric  Railway 
Engineering  Association. 

is  used  as  a  preliminary  to  a  stop  signal  ahead,  it  may  mean  to 
proceed,  prepared  to  stop  before  reaching  the  next  signal. 

The  " proceed"  indication  shows  that  the  track  is  clear,  at 
least  as  far  as  the  next  signal,  and  that  full  speed  may  safely  be 
maintained. 


SIGNALS  FOR  ELECTRIC  ROADS  339 

In  America,  the  "stop"  signal  is  invariably  given  by  a  hori- 
zontal semaphore,  or  by  a  red  light.  There  are  two  possible 
locations  of  the  semaphore  for  this  indication,  with  the  blade  in 
a  horizontal  position,  either  to  the  right  or  to  the  left  of  the  mast; 
but  the  left-hand  position  is  being  adopted  more  at  the  present 
time.  When  semaphore  signals  are  employed  for  day  use,  it  is 
customary  to  have  a  series  of  colored  lenses  mounted  on  a  pro- 
jection of  the  blade,  so  that  they  will  appear  in  front  of  a  lamp 
to  give  the  night  and  the  day  indications  simultaneously. 

The  "  proceed  with  caution  "  indication  is  given  by  a  semaphore 
inclined  at  an  angle  of  45°,  or  by  a  yellow  light,  a  combination  of 
lights,  or  a  light  and  semaphore. 

The  "proceed"  signal  is  a  semaphore  in  a  vertical  position  in 
three-position  signaling,  or  60°  from  the  horizontal  in  two-position 
signaling,  or  a  green  light.  The  former  use  of  a  white  light  for 
"proceed"  has  been  almost  entirely  abandoned,  since  there  is 
great  danger  of  confusion  with  other  lights  along  the  road,  which 
might  give  false  indications  to  the  enginemen.  The  standard 
aspects  in  three-position  signaling,  as  adopted  by  the  American 
Electric  Railway  Engineering  Association,  are  shown  in  Fig.  183. 

Methods  of  Train  Spacing. — The  fundamental  principle  of 
train  operation,  which  is  almost  universally  used  on  railroads,  is 
to  have  successive  trains  separated  by  such  an  interval  that,  in 
the  event  of  an  accident  to  any  train,  the  one  following  will  have 
sufficient  distance  to  stop  before  colliding  with  the  first.  This 
has  been  rigidly  adhered  to  in  all  systems  of  train  dispatching, 
and  is  naturally  the  only  one  which  will  prevent  frequent  colli- 
sions; for  conditions  may  arise  at  any  time  which  make  it  neces- 
sary for  a  train  to  stop  at  an  unexpected  place.  The  exact  dis- 
tance which  must  be  allowed  between  trains  depends  largely  on 
the  maximum  speeds  attained,  as  may  be  seen  by  referring  to 
Chapter  VII. 

Time  Interval  Operation. — The  earliest  method  of  keeping  the 
proper  distance  between  trains  was  to  separate  them  by  a  fixed 
time  interval.  Provided  the  train  speeds  are  the  same,  this  will 
keep  them  at  a  constant  distance  apart,  so  the  proper  interval 
for  allowing  an  emergency  stop  will  always  be  maintained.  But 
if  the  first  train  is  delayed,  there  is  no  way,  after  the  second  one 
has  passed  the  last  station  before  the  forward  one  is  reached,  to 
warn  the  engineer  of  the  following  train  that  the  track  is  occupied. 
This  deficiency  is  presumably  taken  care  of  by  sending  back  a 


340  THE  ELECTRIC  RAILWAY 

flagman  from  the  delayed  train,  who  signals  the  second  one  to 
proceed  under  control,  prepared  to  find  the  other  train  ahead  of 
him.  If  the  first  again  moves  forward  at  its  usual  speed,  the 
proper  distance  will  be  maintained.  The  correct  time  interval 
can  be  regained  when  the  next  station  is  reached. 

This  method  is  open  to  serious  objections.  The  first  train  may 
not  be  stopped,  but  may  be  forced  to  run  at  a  lower  speed  than 
normal.  No  flagman  will  be  sent  back  in  such  a  case,  so  that 
there  will  be  no  protection  for  the  following  train  as  in  the  first 
example.  On  a  curved  track,  where  the  engineman  of  the  follow- 
ing train  cannot  see  the  rear  of  the  for  ward  one,  there  is  great  dan- 
ger of  a  collision.  Such  troubles  have  been  so  frequent  that 
the  method  has  fallen  entirely  into  disfavor. 

Train  Order  Dispatching. — A  modification  of  the  method 
consists  in  placing  the  entire  division  under  the  control  of  a  dis- 
patcher, who  is  responsible  for  the  proper  movement  of  all  trains. 
By  his  direction,  orders  are  issued  to  the  crews,  specifying  meeting 
points  and  trains  liable  to  be  encountered.  Under  no  circum- 
stances is  a  crew  to  proceed  without  obtaining  an  order.  This 
procedure  gives  the  dispatcher  knowledge  of  the  location  of  all 
trains  at  all  times,  and  should  prevent  any  possibility  of  accident. 
The  system  is  usually  worked  in  connection  with  a  published  time- 
table, in  which  case  the  regular  trains,  when  running  on  schedule 
time,  may  be  relieved  from  receiving  special  orders.  The  train- 
order  method  of  dispatching  is  in  very  wide  use  in  this  country, 
and  may  be  termed  the  standard  method  of  operation  for  Ameri- 
can trains.  The  principal  objection  to  it  is  the  danger  of  a  slip 
occurring  in  the  dispatcher's  office,  or  between  him  and  the  crew. 

Two  methods  of  transmitting  train  orders  are  in  general  use: 
the  telegraph  and  the  telephone.  The  former  is  quite  satis- 
factory, and  has  been  in  use  for  many  years.  The  telephone, 
while  it  has  only  been  tried  in  the  last  few  years,  appears  to  have 
the  same  superiority  over  the  telegraph  that  it  has  in  commercial 
work.  It  is  more  rapid,  does  not  require  expert  operators,  and 
gives  a  better  chance  for  direct  communication  with  the  train 
crews,  and  so  informing  them  of  details  which  may  be  overlooked 
with  the  telegraphic  train  order. 

The  Space  Interval. — The  maintenance  of  a  proper  distance 
between  trains,  rather  than  a  fixed  time,  is  evidently  the  scientific 
method  of  protection.  Each  train  carries  in  front  of  it  a  danger 
zone,  determined  by  the  distance  required  for  stopping.  The 


SIGNALS  FOR  ELECTRIC  ROADS  341 

ideal  way  would  be  to  have  this  zone  marked  in  front  of  the  train, 
arranging  that  if  an  obstruction  should  be  encountered,  the 
engineman  would  be  warned,  so  that  he  could  stop  his  train 
within  the  protected  space.  This  is  obviously  impossible;  but 
the  converse  of  the  method,  to  provide  a  danger  zone  behind, 
with  an  arrangement  to  warn  the  following  train,  can  be  provided 
in  a  number  of  different  ways.  It  is  not  necessary  to  make  the 
danger  zone  absolutely  the  smallest  stopping  distance,  unless  the 
traffic  is  so  dense  as  to  render  it  essential.  Any  distance  above 
this  minimum  can  be  employed,  and  the  safety  will  be  even  greater. 
The  simplest  method  of  providing  the  proper  spacing  is  to  di- 
vide the  track  into  a  number  of  sections,  which  must  be  at  least  as 
long  as  the  minimum  stopping  distance.  These  sections  are 
ordinarily  known  as  "  blocks." 

Telegraphic  Block. — The  easiest  way  to  divide  the  track  into 
blocks  is  to  place  signalmen  at  the  proper  points,  providing  them 
with  telegraphic  connection  to  the  signalmen  on  either  side.  The 
general  method  of  operation  is  to  allow  but  one  train  in  a  block  at 
one  time.  Where  it  enters,  the  signalman  reports  to  the  operator 
at  the  other  end  that  he  has  admitted  the  train,  and  the  block  is 
then  closed  to  further  traffic  until  it  is  reported  out  by  the  opera- 
tor at  the  far  end.  The  block  is  then  clear  for  a  train  from  either 
direction,  if  the  road  is  operated  as  a  single-track  line. 

The  condition  of  the  track  is  reported  to  the  engineman  by  word 
of  mouth,  by  a  flag  or  lantern,  or  more  commonly  by  a  fixed  sig- 
nal, consisting  of  a  semaphore  or  target  by  day,  and  a  colored 
light  at  night.  The  signal  can  be  operated  by  hand  or  by  some 
mechanical  method  under  control  of  the  signalman. 

Controlled  Manual  System. — It  is  possible  to  interlock  the  sig- 
nals at  the  two  ends  of  the  block,  so  that,  after  the  signal  has  been 
set  to  protect  a  train,  it  cannot  be  changed  until  the  train  has  been 
reported  out  at  the  other  end  of  the  block.  This  is  accomplished 
by  having  an  electric  interlock  in  the  operating  mechanism,  which 
can  be  released  only  by  a  movement  of  the  controlling  switch  at 
the  other  end  of  the  block.  In  this  form,  it  is  known  as  the  "  con- 
trolled manual  system." 

Automatic  Block  Signals. — Both  the  plain  telegraphic  block 
and  the  controlled  manual  depend  on  the  ability  of  the  operators. 
Although  man-failure  is  fortunately  quite  rare,  there  have  been 
enough  serious  accidents  from  neglect  of  duty,  misunderstanding, 
and  other  similar  causes  to  make  it  desirable  to  have  some  form 


342  THE  ELECTRIC  RAILWAY 

of  control  entirely  independent  of  the  human  factor.  The  most 
logical  arrangement  is  to  have  the  signals  operated  by  the  action 
of  the  train  itself,  in  which  case  the  reliability  depends  on  the 
excellence  of  the  mechanical  devices  used  for  transmitting  the 
information  supplied  by  the  movement  of  the  train. 

All  the  successful  forms  of  automatic  block  signals  use  elec- 
tricity for  transmitting  the  indications.  The  differences  between 
various  systems  depend  on  the  means  used  for  the  transmission, 
and  for  operating  the  signals.  There  are  two  entirely  distinct 
methods  of  controlling  signals  electrically:  by  the  use  of  a 
separate  wire  circuit,  and  by  making  the  rails  the  conductors  of 
the  signal  system.  In  the  latter  method  a  wire  circuit  may 
be  run  as  an  auxiliary. 

Wire  Circuit  Signals. — Signals  employing  a  wire  circuit  are 
used  to  a  considerable  extent  on  the  shorter  interurban  roads, 
and  also  on  city  roads.  The  principle  is  about  the  same  as  that 
of  the  two-way  switch  for  operating  incandescent  lamps.  This 

._     Trolley 

~T~  &ina,Wn  ~T~ 

Lamps  ^Lamp$\ 


Track 


FIG.  184. — Manually  operated  wire  circuit  signal. 

This  contains  the  essential  elements  of  the  widely  used  types  of  trolley-contact  signals. 

arrangement  has  actually  been  applied  to  railway  signaling.  It 
may  be  employed  as  a  manually  operated  device,  as  shown  in  Fig. 
184.  Here  a  single  wire  has  in  its  circuit  a  number  of  incan- 
descent lamps,  sufficient  to  burn  at  about  normal  brilliancy  on 
trolley  pressure.  Each  end  of  the  signal  wire  terminates  in  a 
single-pole,  double-throw  switch,  which,  as  shown,  may  be 
connected  either  to  the  trolley  or  to  the  track.  In  the  position 
given,  with  both  ends  of  the  signal  circuit  grounded,  the  lamps 
will  not  light,  and  the  same  result  occurs  if  both  are  connected 
to  the  trolley.  When  a  train  enters  the  block  at  either  end, 
throwing  the  switch  to  the  opposite  position  will  light  the  lamps  at 
both  ends  of  the  block.  On  leaving,  throwing  the  switch  will 
extinguish  the  lamps.  The  only  difference  will  then  be  that  the 
lamp  circuit  is  connected  to  the  trolley  at  each  end,  while  origi- 
nally it  was  grounded.  It  is  in  the  proper  position  that  when  a 
train  enters  the  block  at  either  end,  the  lamps  can  again  be 


SIGNALS  FOR  ELECTRIC  ROADS  343 

lighted.  This  arrangement  is  suitable  for  single-  or  double-track 
roads,  with  traffic  in  one  or  both  directions,  and  it  is  used  in  this 
form  on  a  number  of  electric  roads,  being  operated  by  hand.  The 
greatest  objection  to  the  manual  signal  is  that  the  car  must  come 
to  a  stop,  and  one  of  the  crew  must  leave  his  position  on  the  train 
to  throw  the  signals. 

A  development  of  this  simple  signal  is  to  have  the  switch 
thrown  automatically,  which  may  be  accomplished  by  a  mechan- 
ical trip,  but  better  by  a  magnet  operated  from  the  trolley  circuit. 
When  desired,  a  semaphore  can  be  used  in  place  of  the  lamps  as  an 
indicator. 

A  modification  of  the  trolley  contact  signal  is  made  in  which  it 
not  only  indicates  whether  a  block  is  occupied  or  not,  but  also 
records  the  number  of  cars  therein,  so  that  the  signals  are  not 
cleared  until  all  the  cars  have  been  counted  out.  This  is  accom- 
plished by  having  the  cars  pass  two  trolley  contacts,  motion  in 
one  direction  notching  up  a  ratchet,  and  in  the  other  direction 
returning  it  toward  its  normal  position.  With  one  such  system 
as  many  as  fifteen  cars  can  be  recorded  in  this  manner. 

In  signal  operation,  it  is  not  sufficient  to  have  the  " proceed" 
indication  given  whenever  the  block  is  clear,  and  the  "stop" 
signal  when  it  is  occupied.  Conditions  may  arise  when  there  is 
no  train  in  the  block  and  yet  it  is  unsafe  for  one  to  proceed. 
Such,  for  example,  are  the  presence  of  a  broken  rail,  an  open 
switch,  or  a  train  on  a  siding  which  is  so  near  the  main  line  that  it 
will  foul  the  track.  If  any  of  these  be  present,  the  signals  should 
give  the  "stop"  indication.  In  general,  such  abnormal  condi- 
tions are  not  indicated  by  signals  of  the  trolley  contact  type.  The 
use  of  this  type  should  therefore  be  limited  to  places  where  the 
liability  of  danger  from  such  sources  is  a  minimum.  Further, 
there  is  a  prevalent  opinion  among  railway  men  that  the  action  of 
the  trolley  contactors  is  not  entirely  satisfactory  at  high  speeds, 
although  the  manufacturers  claim  that  their  operation  is  perfect 
at  speeds  up  to  about  60  miles  per  hr. 

Continuous  Track  Circuit  Signals. — To  care  for  protection  from 
conditions  such  as  are  mentioned  in  the  above  paragraph,  an 
entirely  different  method  of  controlling  the  signals  may  be  used. 
This  is  by  the  use  of  the  track  rails  as  the  conductors  of  the  signal 
system.  The  American  Electric  Railway  Engineering  Associa- 
tion makes  the  following  recommendation:1 

1  Engineering  Manual,  American  Electric  Railway  Engineering  Asso- 
ciation, Section  Ss  7a. 


344  THE  ELECTRIC  RAILWAY 

"For  high-speed  interurban  service,  where  automatic  sig- 
nals are  controlled  by  continuous  track  circuits,  that 
expenditures  be  concentrated  on  the  form  of  indication 
in  preference  to  a  more  expensive  form  of  signal,  and  a 
less  reliable  form  of  control." 

The  original  patent  covering  the  use  of  the  track  circuit  as  a 
control  for  the  signal  system  was  granted  to  William  Hobinson  in 
1872.  The  fundamental  parts  of  this  system  are  shown  in  Fig. 
185.  The  track  is  divided  into  sections  at  the  ends  of  the  blocks, 
the  rails  being  electrically  separated  from  each  other  at  these 
points  by  insulating  joints.  At  the  end  of  the  block  where 
the  train  enters  is  placed  a  relay,  similar  to  the  ordinary 
telegraph  relay;  while  at  the  opposite  end  is  a  closed-circuit 
battery  of  the  proper  size.  When  there  is  no  train  in  the  block, 
and  the  continuity  of  the  track  circuit  is  perfect,  a  current  will 


Track  Rails' 


Battery 


'firoceeer 

FIG.  185. — Simple  track  circuit. 

In  this  form,  the  track  circuit  signals  have  been  installed  on  a  great  many  lines  of  double- 
track  steam  railroad. 

flow  from  the  battery  through  the  rails,  energizing  the  relay. 
This  operates  a  local  circuit  at  the  signal  to  give  the  "proceed" 
indication.  If  a  train  enters  the  block,  the  wheels  and  axles 
place  a  short-circuit  on  the  battery,  and  the  relay  is  de-energized. 
This  causes  the  auxiliary  circuit  to  open,  giving  the  "stop" 
indication.  It  is  evident  that  the  same  result  is  obtained  if  a 
broken  rail  exists  in  the  block.  By  including  all  switches  in  the 
circuit,  and  connecting  the  rails  of  sidings  back  to  a  point  beyond 
the  fouling  limits,  protection  is  obtained  from  these  sources  of 
danger. 

The  original  Robinson  device  is  suitable  for  the  protection  of 
steam  roads,  on  which  the  traffic  is  always  in  one  direction.  It  is 
the  basis  of  all  modern  signal  systems  using  the  track  for  the  con- 
trol circuit.  There  are  a  number  of  objections  to  the  system, 
none  of  which  is  particularly  serious.  The  operation  depends  on 


SIGNALS  FOR  ELECTRIC  ROADS  345 

the  insulation  between  the  rails  being  maintained  at  a  fairly  high 
value,  since  the  fundamental  idea  is  to  have  sufficient  current 
reach  the  relay  to  energize  it  when  the  block  is  clear.  Although 
but  a  few  volts  are  used,  the  leakage  of  current  during  wet  weather 
is  considerable.  A  larger  number  of  cells  in  series  does  not  aid 
much,  since  the  leakage  is  increased  somewhat  faster  than  in  pro- 
portion to  the  e.m.f.  Of  the  total  output  of  the  battery,  about  40 
per  cent,  is  used  to  operate  the  relay,  the  remainder  being  used  to 
overcome  the  resistance  of  the  track  circuit  and  to  supply  leakage. 

Track  Circuits  for  Electric  Railways. — The  direct-current  track 
circuit,  as  described,  is  not  suitable  for  electric  railways  if  the 
rails  are  to  be  used  for  carrying  the  propulsion  current,  since  even 
a  small  current  due  to  train  operation  may  be  enough  to  give  false 
indications  of  the  signals.  In  order  to  make  the  track  circuit 
applicable  for  electric  railway  signaling,  it  is  necessary  to  make  a 
radical  change  in  some  of  the  details. 

The  difficulty  due  to  the  presence  of  current  in  the  track  can  be 
overcome  by  using  a  different  kind  in  the  signal  circuit,  and 
employing  a  relay  which  responds  only  to  that.  For  instance, 
on  roads  having  direct  current  for  propulsion,  alternating  current 
is  suitable  for  signaling,  and  a  relay  of  the  induction  type,  which 
does  not  respond  to  direct  current,  may  be  employed. 

Single  Rail  System. — Another  difficulty  in  the  use  of  track 
circuits  for  electric  railway  signaling  is  that  the  rails  must  be 
made  continuous  if  they  are  to  carry  the  main  current.  If  condi- 
tions are  such  that  the  conductivity  of  one  rail  is  sufficient  for  the 
purpose,  or  if  auxiliary  conductors  can  be  installed,  one  of  the 
track  rails  can  be  used  for  carrying  the  line  current,  while  the 
other  is  cut  into  insulated  sections  to  form  the  signal  blocks. 
The  arrangement  of  circuits  is  shown  in  Fig.  186.  It  may  be  seen 
that  a  lowering  transformer  replaces  the  battery  of  the  direct- 
current  signal  circuit,  a  supply  of  alternating  current  being 
furnished  by  the  signal  mains.  To  limit  the  current  which  can 
flow  when  a  large  difference  of  potential  exists  in  the  return  con- 
ductor rail  between  the  ends  of  the  block,  a  certain  amount  of 
non-inductive  resistance  is  inserted  in  the  circuit.  To  prevent 
any  magnetizing  action  from  what  direct  current  does  pass 
through  the  signal  apparatus,  the  transformer  is  made  with  an 
air-gap,  and  a  reactance  coil,  also  with  an  air-gap,  is  shunted 
across  the  terminals  of  the  relay.  The  action  of  the  latter  is 
like  that  in  the  direct-current  signal  system,  but  the  type  is 


346 


THE  ELECTRIC  RAILWAY 


different,  being  similar  to  a  single-phase  induction  motor.  The 
action  of  the  signal  mechanism  may  be  the  same  as  with  direct- 
current  track  circuits;  but,  since  a  supply  of  alternating  current 
is  present  for  the  track  circuit,  it  is  simpler  to  use  it  throughout, 
induction  motors  being  employed  for  operating  semaphores. 
When  lamps  are  used  for  the  indications,  they  can  be  supplied 
from  the  signal  mains  through  lowering  transformers. 

It  is  evident  that  the  same  protection  is  given  with  this  system 
as  with  the  direct-current  track  circuit.  A  broken  rail  or  a  fouled 
switch  can  be  made  to  indicate  equally  well.  The  principal 
objection  is  that  only  one  of  the  track  rails  is  available  for  the 
return  circuit;  and  in  some  cases  additional  feeders  must  be 
installed.  For  an  elevated  or  a  subway  line,  this  defect  is  not 


Re  f urn  Current  Rail 


FIG.  186. — Single-rail  alternating-current  signal  circuit. 


This  type  of  track-circuit  signal  is  suitable  for  electric  roads  using  direct  current,  or  for 
eteam  roads  where  there  is  danger  of  interference  from  stray  current  in  the  rails. 

serious,  since  the  metal  structure  can  be  used  to  supplement  the 
track;  but  for  an  interurban  road  the  cost  of  additional  copper 
may  be  prohibitive. 

For  steam  roads,  the  alternating-current  system  is  finding  more 
favor  at  present  than  the  direct,  since  stray  direct  currents  due  to 
leakage  from  electric  lines  are  liable  to  derange  the  signal  circuits. 
This  may  be  obviated  by  the  use  of  alternating  current  for  operat- 
ing the  signals,  as  described  above.  In  this  case  both  rails  may  be 
divided  into  insulated  sections. 

Double  Rail  Alternating-Current  System. — If  the  propulsion 
current  can  be  prevented  from  interfering  with  the  action  of  the 
signal  mechanism,  it  will  do  no  harm  in  the  rails;  but  to  keep  the 
blocks  separate  is  a  more  difficult  matter.  The  method  already 


SIGNALS  FOR  ELECTRIC  ROADS 


347 


described  sacrifices  the  conductivity  of  one  rail.  Another  way  is 
to  use  a  form  of  bond  which  will  pass  direct  current,  but  will  not 
allow  alternating  current  to  flow  through.  Such  a  bond  may  be 
made  by  the  use  of  balanced  inductances.  The  arrangement  is 
shown  in  Fig.  187.  The  insulated  joints  are  retained,  as  with  the 
direct-current  track  circuit,  but  the  two  rails  in  each  block  are 
connected  by  inductance  coils,  which  are  joined  together  at  their 
middle  points.  The  obstruction  to  the  flow  of  direct  current  is 
small,  since  the  resistance  of  the  bonds  is  low;  but  there  is  no 
tendency  for  the  alternating  current  to  pass  such  a  bond,  for  the 
two  sides  of  the  track  in  the  adjacent  block  are  balanced. 

If  the  direct  current  is  evenly  divided  between  the  two  rails, 
the  unbalancing  in  the  inductive  bonds  is  negligible;  but  when  the 


Insulated 


FIG.  187. — Double-rail  alternating-current  signal  circuit. 
Suitable  for  use  with  direct  or  alternating  propulsion  current. 

difference  between  the  currents  carried  by  the  rails  is  large,  it  is 
necessary  to  introduce  an  air-gap  into  the  core  of  the  bond  to  lower 
the  inductance.  The  more  perfect  balancing  of  the  potential  drop 
between  the  two  rails  renders  the  use  of  an  air-gap  in  the  magnetic 
circuit  of  the  lowering  transformer  unnecessary,  and  makes  it  pos- 
sible to  dispense  with  the  regulating  resistance  and  with  the  re- 
actance shunting  the  relay,  as  used  in  the  single-rail  system.  A 
similar  induction  relay,  which  responds  only  to  alternating  cur- 
rent, is  employed.  The  other  parts  of  the  apparatus  can  be  the 
same  as  for  any  form  of  track  circuit  signals. 

As  described,  the  alternating-current  track  circuit  signal 
system  is  suitable  for  use  in  connection  with  roads  employing 
direct  current  for  propulsion.  It  is  equally  applicable  to  single- 


348  THE  ELECTRIC  RAILWAY 

phase  or  three-phase  lines,  provided  the  frequency  of  the  signal 
circuit  is  so  chosen  that  the  inductive  bonds  will  pass  the  pro- 
pulsion current,  while  holding  back  that  for  operating  the  signals. 
This  can  be  accomplished  by  using  a  higher  frequency  for  the 
signal  system,  with  an  amount  of  inductance  in  the  bonds  which 
has  a  small  effect  at  the  line  frequency.  For  25-cycle  roads,  60- 
cycle  signaling  current  is  entirely  satisfactory  in  actual  service. 

Methods  of  Operating  Semaphores. — When  semaphores  are 
used  for  the  daylight  indication,  it  is  necessary  to  have  a  more 
complicated  mechanism  for  operating  them  than  is  employed 
with  lights  alone.  The  semaphore  usually  consists  of  a  wooden 
blade,  pivoted  at  one  end,  and  counterweighted  so  that  the  un- 
balanced mass  is  small.  When  arranged  for  use  in  an  upper  quad- 
rant, the  blade  is  slightly  heavier  than  the  counterweight,  so 
that  it  will  fall  to  the  "stop"  indication  if  the  mechanism  fails 
to  hold  it  at  " proceed"  for  any  reason,  whether  in  the  normal 
operation  of  the  system,  or  through  failure  of  the  signal  apparatus. 
On  the  other  hand,  semaphores  for  indication  in  the  lower  quad- 
rant have  the  counterweight  the  heavier,  producing  the  same 
result.  The  great  advantage  of  the  upper  quadrant  signal  is  that 
if  the  blade  is  weighted  with  a  coating  of  ice  sufficient  to  prevent 
operation,  the  blade  will  fall  to  the  "stop"  indication  rather  than 
to  "  proceed."  This  is  a  safety  precaution  which  has  great  value, 
and  is  extending  the  use  of  upper  quadrant  signals. 

The  semaphore  is  ordinarily  moved  to  the  "  proceed  "  indication 
by  a  small  electric  motor,  driven  by  batteries  in  direct-current 
signaling,  and  by  a  transformer  from  the  signal  mains  in  the  alter- 
nating-current systems.  After  the  proper  movement  is  made,  the 
motor  is  automatically  disconnected,  and  the  blade  held  in  posi- 
tion by  an  electromagnet.  In  all  types  of  signals  the  appa- 
ratus is  so  arranged  that  a  failure  of  the  operating  current,  or  of 
any  part  of  the  mechanism,  will  cause  the  signal  to  give  the  "stop  " 
indication. 

Permissive  Operation. — The  signals  discussed  so  far  are  of  the 
absolute  type.  That  is,  the  indication  is  either  "stop"  or  "pro- 
ceed." There  may  be  many  instances  where  it  is  not  necessary 
for  the  train  to  stop  and  remain  at  the  signal,  but  where  movement 
with  extreme  caution  will  be  sufficient  to  guard  against  accident. 
In  any  of  the  absolute  systems,  such  as  those  described,  permis- 
sion may  be  given  by  the  operating  rules  to  disregard  the  signal 
indication  under  certain  conditions.  When  a  train  is  halted  by 


SIGNALS  FOR  ELECTRIC  ROADS  349 

a  signal  set  against  it,  the  indication  may  be  due  to  an  open  switch, 
a  broken  rail,  or  a  train  on  a  siding  within  the  fouling  limits. 
To  save  time,  the  engineman  is  allowed,  after  having  waited  a 
reasonable  length  of  time,  to  enter  and  proceed  slowly,  being 
prepared  to  stop  short  of  any  obstruction.  If  a  train  is  in  the 
block,  it  is  still  protected  by  the  slow  speed  of  the  second  train, 
and  if  one  of  the  accidental  conditions  is  encountered,  or  the 
signal  mechanism  is  out  of  order,  it  can  be  reported  by  the  train 
crew.  When  operated  in  this  manner  the  signal  system  becomes 
permissive  to  a  limited  extent. 

Preliminary  Signals. — It  is  not  always  possible  to  locate  the 
signals  at  such  points  that  they  may  be  seen  for  great  distances 


Home  Distant  Horns  Distant  Home 

FIG.  188. — Use  of  distant  signals. 

The  home  signal  is  repeated  at  a  point  far  enough  ahead  that  the  engineer  can  get  his 
train  under  control,  prepared  to  stop  when  necessary  before  reaching  the  home  signal. 

along  the  track.  In  order  to  be  effective,  the  distance  which  a 
signal  can  be  observed  by  the  engineman  must  be  sufficient  to 
permit  stopping  the  train  before  passing  it.  If  there  are  obstruc- 
tions along  the  track,  it  may  be  necessary  to  repeat  the  indication 
at  some  point  in  advance  of  the  signal.  The  arrangement  is 
shown  in  Fig.  188.  The  indication  of  the  home  signal  js  merely 


FIG.  188. — Combined  home  and  distant  signals. 

The  operation  is  the  same  as  shown  in  Fig.  188;  this  arrangement  is  used  when  the  blocks 
are  short  enough  to  warrant  it. 

repeated,  but  it  is  read  differently.  The  distant  signal  in  the 
forward  block  shown  may  be  read:  " Proceed  at  full  speed;  ex- 
pect to  find  the  next  home  signal  in  'proceed'  position.''  The 
distant  signal  in  the  rear  block  indicates:  " Proceed,  prepared 
to  stop  at  the  next  honie  signal.''  If  the  distant  signal  is  placed 
at  least  as  far  as  the  stopping  distance  ahead  of  the  home  signal, 
ample  warning  is  given  the  engineman  to  get  his  train  under 
control.  If,  in  the  meanwhile,  the  train  occupying  the  block 


350  THE  ELECTRIC  RAILWAY 

ahead  has  passed  out  of  it,  the  engineman  of  the  second  train  can 
resume  full  speed  as  soon  as  he  sees  the  " proceed"  indication  of 
the  home  signal. 

When  the  blocks  are. necessarily  short,  it  becomes  more  eco- 
nomical to  mount  the  two  semaphores  on  a  single  mast,  or  to  com- 
bine them  in  a  single  three-position  signal.  In  the  latter  case, 
the  arrangement  is  shown  in  Fig.  189.  The  indications  are  as 
before;  but  the  same  semaphore  may  give  both  the  distant  indi- 
cation for  the  block  ahead,  and  the  home  indication  for  its  own. 

Signals  for  Operation  in  Two  Directions. — The  signals  so  far 
considered  are  all  designed  for  normal  operation  in  one  direction 
only,  or,  in  other  words,  for  double-track  roads.  To  provide 
an  absolute  block  system  for  a  single  track  does  not  present  much 


FIG.  190. — Single-track  signaling.    Positions  of  semaphores  for  following 

cars. 

additional  difficulty,  requiring  principally  that  arrangement  be 
made  to  show  the  proper  indication  at  each  end  of  the  block, 
instead  of  at  one  end  only.  A  simple  method  of  accomplishing 
this  is  to  place  the  battery  or  transformer  supplying  the  track 
circuit  at  the  center  of  the  block  with  relays  at  each  end.  The 
conductance  of  the  train  is  so  much  greater  than  that  of  the  relay, 
that  if  the  size  of  battery  or  transformer  is  properly  chosen,  the 
presence  of  a  train  will  prevent  enough  current  reaching  the  relay 
to  operate  it,  so  that  the  signals  at  both  ends  of  the  block  will 
give  the  "stop"  indication.  While  this  arrangement  will  give 
protection,  and  can  be  used  with  or  without  preliminary  signals, 
it  limits  the  capacity  of  the  block  to  one  train  at  a  time.  It  is 
possible  to  operate  several  trains  in  the  same  direction  in  one 
block,  provided  the  signals  will  give  proper  protection;  but,  with 


SIGNALS  FOR  ELECTRIC  ROADS  351 

the  ordinary  types  controlled  by  the  track  circuit,  it  is  not  easy 
to  do  this. 

A  recent  type  of  track  circuit  signal  is  arranged  to  give  control 
so  that  two  cars  may  be  in  a  block  between  sidings,  if  moving  in 
the  same  direction,  while  they  must  be  spaced  a  distance  apart 
at  least  one-half  of  the  total  block  length.  The  arrangement  of 
signals  in  this  system  is  given  in  Fig.  190,  the  progression  of  two 
following  cars  through  the  blocks  being  shown,  while  in  Fig.  191 
the  movement  of  two  opposing  trains  is  seen.  Details  of  the 
equipment  and  methods  of  operation  are  given  in  recent  issues 
of  the  Electric  Railway  Journal.1 


FIG.  191.  —  Single-track  signaling.    Positions  of  semaphores  for  opposing 


Cab  Signals.  —  In  bad  weather,  there  is  always  difficulty  in 
observing  the  indications  given  by  roadside  signals.  This  condi- 
tion calls  for  extreme  care  on  the  part  of  the  engineman  to  pre- 
vent running  past  them.  In  extremely  bad  weather,  it  may  be 
necessary  to  reduce  the  running  speed;  and  some  serious  acci- 
dents have  occurred  through  inability  of  the  engineman  to  ob- 
serve the  signals. 

*A  New  System  for  Track  Circuit  Signaling  Without  Preliminaries; 
Electric  Railway  Journal,  Vol.  XLIII,  p.  199,  January  24,  1914. 

A  New  Method  of  Traffic  Acceleration  on  the  Scranton  &  Binghamton; 
Electric  Railway  Journal,  Vol.  XLIV,  p.  602,  October  3,  1914. 


352  THE  ELECTRIC  RAILWAY 

If  the  signal  indications  can  be  given  in  the  locomotive  cab, 
instead  of  at  a  fixed  point  along  the  track,  it  is  evident  that  run- 
ning conditions  will  be  considerably  improved,  especially  in  bad 
weather.  This  has  been  accomplished  in  at  least  one  system. 
The  operation  is  quite  similar  to  that  of  a  trolley  contact  signal, 
the  connection  being  made  by  a  ramp  alongside  the  track,  which 
presses  against  a  shoe  on  the  car  or  locomotive.  By  this  means 
an  indication  is  given  which  is  the  same  as  the  corresponding 
one  at  the  fixed  signal.  It  may  be  operated  by  a  track  circuit, 
the  action  of  the  ramp  being  controlled  thereby;  or  the  ramp  may 
be  used  in  connection  with  a  trolley  contact. 

Cab  signals  possess  the  advantage  of  presenting  the  indication 
to  the  engineman  at  all  times,  so  that  there  is  no  valid  excuse  for 
running  past  a  "stop'7  signal.  This  feature  is  one  which  is 
worthy  of  considerable  attention  from  railway  operators. 

The  Automatic  Stop. — For  many  years  it  has  been  desired  to 
have  a  suitable  means  of  absolutely  preventing  disregard  of  the 
signal  indications.  On  all  railroads  some  form  of  surprise  test 
is  made  at  irregular  intervals  to  determine  whether  the  indica- 
tions are  being  obeyed.  This  arrangement,  while  getting  better 
service,  is  a  crude  way  of  checking  the  effectiveness  of  the  signal 
system.  A  method  which  absolutely  prevents  improper  opera- 
tion is  the  best,  and  next  to  that  is  the  determination  of  every 
infringement  of  the  rules. 

Methods  of  stopping  trains  which  run  past  danger  signals  have 
usually  been  confined  to  devices  for  applying  the  emergency 
brakes.  The  earliest  arrangement  consisted  of  a  glass  tube  con- 
nected to  the  air-brake  system,  and  mounted  on  the  roof  of  the 
car  or  locomotive  in  such  a  position  that  it  would  strike  an  arm 
projecting  from  the  semaphore  blade,  and  moved  therewith. 
Passing  of  a  "stop"  signal  breaks  the  glass,  and  applies  the  emer- 
gency brake.  If  a  tube  has  been  broken,  it  must  be  replaced  with 
a  good  one  in  order  that  the  train  may  proceed.  A  duplicate  tube 
is  furnished  each  train  crew;  but  the  fact  that  one  has  been  broken 
is  an  indication  in  itself  that  the  signal  has  been  disobeyed.  A 
modification  of  the  system,  in  use  in  the  subways  and  tunnels 
around  New  York  City,  is  identical  in  principle,  but  employs  a 
mechanical  trip  projecting  from  the  roadbed,  which  opens  a 
valve  on  the  train. 

It  is  usually  desirable  to  make  the  automatic  stop  permissive, 
in  the  same  way  that  the  fixed  signal  is  permissive.  To  do  this, 


SIGNALS  FOR  ELECTRIC  ROADS  353 

an  arrangement  must  be  made  so  that  the  train  crew  can  unlock 
the  stop,  and  proceed  by  it,  when  allowed  under  the  rules.  This 
may  readily  be  done;  and  it  prevents  loss  of  time  in  case  a  false 
indication  is  given,  or  if  any  of  the  abnormal  conditions  which 
may  exist  are  present. 

Automatic  Train  Control. — It  is  but  a  short  step  from  the  auto- 
matic stop  to  the  entire  automatic  control  of  train  operation. 
The  former,  as  described,  will  stop  a  train  only  when  it  has  already 
passed  a  "  stop  "  signal.  It  is  possible  that  the  train  which  causes 
the  indication  is  directly  ahead  of  the  signal,  in  which  case  there 
would  be  no  additional  protection  due  to  the  automatic  stop. 
To  make  the  latter  effective  in  such  emergencies,  the  stop  should 
be  located  at  the  distant  or  preliminary  signal.  This,  again,  has 
the  disadvantage  that  if  the  block  should  be  cleared  before  the 
train  reaches  the  home  signal,  the  operation  of  the  stop  will  cause 
an  unwarranted  delay.  The  ideal  control  is  to  have  a  form  of 
trip  operated  in  such  a  manner  that  it  will  cause  the  train  to 
reduce  speed  on  passing  a  distant  signal  giving  the  "  proceed  with 
caution"  indication,  but  not  forcing  a  stop  unless  the  train  over- 
runs a  home  signal  displaying  "  stop."  By  this  method  the  speed 
of  the  train  will  be  under  control  from  the  time  the  distant  signal 
is  passed,  whether  the  engineman  obeys  the  indication  or  not. 

Up  to  the  present  time,  no  system  has  been  developed  which  has 
proved  entirely  satisfactory.  In  a  prize  competition  held  by  the 
New  Haven  road  a  few  years  ago,  no  less  than  1800  entries  were 
made.  From  the  amount  of  interest  in  the  subject,  as  evidenced 
by  this  large  number  of  competitors,  it  would  seem  that  a  satis- 
factory solution  of  the  problem  may  be  made  within  the  next  few 
years. 

Interlocking. — At  points  where  several  lines  of  railroad  track 
diverge,  or  where  roads  intersect,  there  is  an  exceptionally 
dangerous  situation.  In  many  cities,  where  the  lines  cross  steam 
railroad  tracks  at  grade,  it  is  customary  to  have  a  flagman,  or  to 
have  one  of  the  train  crew  flag  the  car  across  the  tracks.  This 
slows  down  the  schedule  speed  considerably,  and  is  not  absolutely 
safe,  especially  where  there  are  but  few  steam  trains.  Interurban 
and  steam  railroads  usually  guard  their  tracks  against  collisions 
by  the  use  of  interlocking  plants  at  the  points  of  intersection. 

The  interlocking  plant  consists  of  a  set  of  "stop"  signals,  so 
interconnected  that  it  is  impossible  to  give  the  "proceed"  in- 
dication on  conflicting  routes.  Combined  with  this  is  a  set  of 
23 


354  THE  ELECTRIC  RAILWAY 

derailing  switches  to  prevent  the  progress  of  trains  which  might 
disregard  the  "stop"  signals.  Detector  bars  are  usually  em- 
ployed to  prevent  a  rearrangement  of  the  signals  while  a  train  is 
in  the  act  of  passing  the  intersection.  By  these  precautions,  a 
collision  is  impossible,  even  when  the  indications  are  disregarded, 
unless  the  apparatus  is  out  of  order. 

The  operation  of  the  interlocking  apparatus  may  be  accom- 
plished by  several  methods.  The  simplest  of  these  is  the  plain 
mechanical  interlocking  machine,  which  has  been  in  service 
on  many  roads  for  years.  The  power  for  operation  is  supplied  by 
a  signalman,  who  is  located  in  a  tower  where  he  can  see  the  entire 
set  of  tracks  under  his  supervision.  The  levers  of  the  mechanical 
machine  are  somewhat  heavy,  and  require  a  considerable  amount 
of  force  to  operate.  The  movement  is  necessarily  slow. 

Improvements  on  the  mechanical  interlocking  machine  have 
been  mainly  in  the  substitution  of  some  easily  controlled  power 
for  manual.  The  most  successful  forms  of  power  interlocking 
machines  are  the  electric  and  the  electropneumatic.  The 
methods  of  operation  of  the  two  are  almost  identical,  the  main 
difference  being  that  in  one  compressed  air  is  employed  for  throw- 
ing the  switches  and  signals,  while  in  the  other  electric  motors 
and  electromagnets  are  used.  In  both  the  movement  is  con- 
trolled electrically. 

The  principal  advantages  of  power  interlocking  of  the  two  kinds 
mentioned  are  that  the  time  of  operation  is  reduced  by  about  one- 
half,  that  the  space  required  in  the  interlocking  tower  is  but  about 
one-fourth,  that  the  number  of  operators  is  materially  reduced, 
and  the  space  needed  for  connections  between  the  tower  and  the 
signals  and  switches  is  much  less.  These  advantages  are  suffi- 
cient to  justify  the  use  of  power  apparatus  in  any  but  the  smallest 
plants. 


CHAPTER  XVII 
SYSTEMS  FOR  ELECTRIC  RAILWAY  OPERATION 

As  was  stated  in  the  first  chapter,  there  are  several  possible 
combinations  of  electric  circuits  and  motors  for  the  operation  of 
railway  trains.  The  various  elements  have  been  considered 
separately,  and  it  now  remains  to  bring  together  the  details 
which  make  up  the  complete  systems.  Of  the  possible  combina- 
tions, the  direct-current,  the  three-phase,  and  the  single-phase 
circuits  have  been  used  for  supplying  the  propulsion  current  to 
the  cars.  These  will  be  taken  up  in  order,  so  that  the  merits  of 
each  can  be  discussed. 

6oo-Volt  Direct-current  System. — This  is  the  oldest  type  of 
electric  railway  distribution  at  present  in  use.  As  has  been 
mentioned  in  previous  chapters,  it  is  a  gradual  development  from 
the  low-pressure  circuits  with  which  the  early  roads  were  equipped 
and  represents  about  the  safe  limit  of  potential  for  continuous 
operation  of  motors  without  interpoles. 

The  motors  used  are  almost  invariably  of  the  series  type. 
Due  to  the  long  period  of  development,  they  are  well  standard- 
ized, and  the  minor  defects  have  been  eliminated  to  a  large  extent. 
No  more  reliable  and  satisfactory  motors  are  known  for  use  on 
railway  circuits.  The  direct-current  series  motor,  when  adapted 
for  railway  operation,  is  as  light  as  any,  and,  since  the  parts  are 
comparatively  simple,  it  is  one  of  the  cheapest  motors  avail- 
able. Furthermore,  the  standard  machines  are  quite  effi- 
cient, although  no  attempts  have  been  made  to  attain  the  very 
highest  efficiency.  Ruggedness  and  freedom  from  breakdowns 
have  been  considered  more  desirable  than  refinements. 

The  series  motor  has  a  great  advantage  over  other  types,  in 
that  it  automatically  protects  itself  against  overloads.  Since 
the  same  current  flows  through  both  armature  and  field,  a  sudden 
load  thrown  on  the  machine  cannot  cause  a  great  increase  in 
armature  current  without  a  corresponding  gain  in  field  strength, 
so  that  the  motor  slows  down  when  an  overload  is  encountered, 
and  does  not  draw  such  a  great  rush  of  current  as  do  other  types 
under  similar  conditions.  With  the  addition  of  interpoles,  the 

355 


356  THE  ELECTRIC  RAILWAY 

troubles  due  to  overload  and  to  variation  of  the  supply  potential 
are  minimized  to  a  point  where  they  have  practically  no  effect 
on  the  satisfactory  operation  of  the  machines. 

If  a  need  arises,  as  for  instance  to  get  characteristics  suitable 
for  regeneration,  the  shunt  motor  can  be  used;  and  if  desired,  the 
compound  motor  is  also  available  for  operation  on  the  direct- 
current  circuit.  In  this  way,  speed  characteristics  of  any  form 
whatever  may  be  obtained  with  this  system,  although  up  to  the 
present  time  the  series  motor  has  fulfilled  all  requirements. 

The  control  of  direct-current  motors,  while  quite  satisfactory, 
is  scarcely  up  to  the  standard  set  by  the  motors  themselves. 
It  has  been  shown  that  there  is  a  considerable  loss  of  energy  in 
the  resistors  while  starting,  which  is  an  inherent  defect,  and 
which  cannot  be  remedied  without  the  use  of  very  special  methods 
which  are  so  complicated  as  to  have  but  limited  application. 
With  the  ordinary  forms  of  series-parallel  control,  there  are  but 
two,  or  at  best  three,  efficient  operating  speeds.  By  the  use  of 
field  control,  as  many  more  speeds  may  be  added  at  the  cost  of  a 
slight  complication  of  the  circuits.  Field  control  also  reduces  the 
energy  consumption  when  direct-current  motors  are  used  for 
mixed  service,  such  as  combined  city  and  interurban  lines. 

The  contact  line  is  extremely  simple.  Either  the  third  rail  or 
the  overhead  trolley  may  be  used,  or,  if  special  conditions  de- 
mand it,  the  underground  conduit  or  perhaps  surface  contact  can 
be  satisfactorily  employed.  While  these  special  forms  of  contact 
conductor  might  be  used  with  other  distribution  circuits,  they  are 
not  suited  to  higher  potentials,  which  form  the  basis  of  all  the 
other  systems. 

The  low-tension  distribution,  which  is  responsible  for  the  ex- 
treme simplicity  of  the  600-volt  system,  is  in  itself  the  great 
source  of  inefficiency.  The  loss  in  the  distributing  circuit  is 
necessarily  large,  whether  in  energy  when  a  small  expenditure  for 
copper  is  made,  or  in  overhead  cost  when  a  larger  conductor  is 
used.  This  is  the  great  drawback  to  the  universal  application  of 
the  system.  It  is  so  serious  that,  even  for  city  roads  of  compara- 
tively great  congestion  and  short  length,  it  is  necessary  to  gener- 
ate alternating  current  for  the  economy  it  offers  in  high-tension 
transmission,  and  to  add  the  somewhat  complicated  and  inefficient 
link  of  lowering  transformers  and  rotating  converting  equipment. 

An  incidental  disadvantage,  which  is  exceedingly  difficult  to 
completely  combat,  is  the  trouble  caused  other  corporations  who 


SYSTEMS  FOR  ELECTRIC  RAILWAY  OPERATION  357 

have  metal  structures  buried  in  the  soil,  by  electrolysis.  The 
low-potential  distribution  is  a  great  contributing  factor  in  this, 
since  it  calls  for  large  currents  to  be  transmitted  through  the  rails, 
unless  an  insulated  return  circuit  is  provided.  While  it  is  con- 
ceded that,  with  great  care,  electrolysis  can  be  prevented,  it  is 
difficult  to  maintain  the  grounded  return  circuit  in  such  ex- 
cellent condition  that  trouble  is  not  liable  to  arise  almost  without 
warning. 

In  spite  of  the  disadvantages,  the  excellence  of  the  600-volt 
system  is  such  that  it  has  been  universally  used  for  city  service, 
and  for  this  class  of  operations  it  is  unquestionably  without  an 
equal.  It  is  not  probable  that  any  other  method  of  distribution 
will  be  advanced  which  will  drive  the  600-volt  system  out  of  this 
field.  For  interurban  service  it  has  been  in  the  past  nearly  always 
adopted;  but  the  use  of  higher  potentials  will  probably  supersede 
the  low-tension  system  more  and  more  where  the  length  of  dis- 
tribution is  great. 

High-Tension  Direct-Current  Systems. — The  use  of  direct 
current  at  higher  potentials  has  followed  the  need  for  a  reduction 
of  the  loss  in  the  distributing  circuit,  especially  for  long  lines. 
Motors  of  the  interpole  type  must  be  employed,  and  the  use  of 
higher  potentials  has  been  entirely  dependent  on  the  development 
of  this  kind  of  machine.  They  possess  the  same  excellent  char- 
acteristics as  the  600-volt  motors;  and,  in  fact,  where  a  1200-volt 
contact  line  is  used,  there  is  no  difference  in  their  construction 
save  the  need  for  more  insulation.  On  account  of  this,  the  out- 
put of  a  given  motor  must  be  somewhat  less  when  wound  for  use 
on  the  higher  pressure,  so  that  the  motors  are  not  so  light,  so 
cheap,  or  so  efficient  when  so  arranged.  The  difference  for  1200- 
volt  operation  is  comparatively  small,  so  that  no  great  effect  due 
to  this  cause  is  apparent.  When  the  motors  are  wound  directly 
for  the  1200-volt  circuit,  the  difference  is  greater;  but  since  this 
change  is  usually  made  to  permit  the  use  of  a  contact  line  at  2400 
volts,  it  is  entirely  justified. 

The  control  for  the  higher  potentials  is  more  expensive  than 
for  600-volt  equipment.  The  arcs  are  more  difficult  to  break,  so 
that  greater  distances  between  the  switch  blades,  better  magnetic 
blowouts,  and  longer  arc  chutes  are  required.  It  is  sometimes 
even  necessary  to  place  two  breaks  in  series  to  prevent  damage 
from  the  arcs.  On  account  of  the  smaller  current,  when  the 
energy  to  be  dissipated  remains  the  same,  the  resistors  used  must 


358  THE  ELECTRIC  RAILWAY 

be  of  smaller  cross-section  and  greater  length.  This  leads  to  a 
more  expensive  and  less  rugged  design. 

The  great  advantage  in  the  high-tension  system  lies  in  the  sav- 
ing in  cost  of  the  contact  line,  either  of  the  conductor  or  of  the 
energy  lost  in  it.  This  is  the  cause  of  the  adoption  of  the  higher 
potentials.  In  the  lines  so  far  constructed,  it  has  not  been  found 
practical  to  generate  direct  current  at  the  contact  line  potential; 
but  alternating-current  generation,  with  high-tension  transmis- 
sion and  conversion  to  direct  current  through  rotating  machinery, 
has  been  adhered  to.  The  highest  potential  at  present  in  use  on 
the  contact  line  is  2400  volts,  while  one  installation  for  operation 
at  3000  volts  is  now  being  constructed.  These  values  are  still  far 
less  than  those  which  have  been  considered  suitable  for  trans- 
mission; and  even  if  decidedly  higher  contact  line  pressures  are 
used,  it  does  not.  seem  likely  that  this  link  in  the  electric  system 
can  be  eliminated. 

One  possibility,  which  has  been  increasing  in  importance  in  the 
past  few  years,  is  the  use  of  mercury  vapor  converters  for  pro- 
ducing a  unidirectional  current  for  the  contact  line  and  motor 
operation.  While  it  is  yet  too  early  to  make  any  definite  state- 
ments, it  may  improve  the  efficiency  of  conversion  by  a  large 
amount. 

A  minor  disadvantage  in  all  the  high-tension  direct-current 
systems  is  the  difficulty  of  obtaining  suitable  current  for  the 
operation  of  auxiliaries,  such  as  air  compressors,  lights,  heaters 
and  minor  apparatus.  In  some  cases  the  pressure  has  been  cut 
down  directly  by  the  use  of  resistance,  while  in  others  special 
dynamotors  and  motor-generators  have  been  used  to  transform 
to  a  lower  potential.  None  of  the  solutions  thus  far  advanced 
seems  entirely  satisfactory. 

In  any  of  the  direct-current  systems,  the  return  of  energy  to 
the  electric  circuit  is  difficult,  unless  motors  with  a  shunt  char- 
acteristic are  employed.  Since  one  of  the  advantages  which 
has  always  been  claimed  for  direct  current  is  the  use  of  motors  of 
the  series  type,  it  would  mean  an  entire  revolution  in  operating 
methods  to  make  the  complete  change  to  shunt  motors.  By 
the  use  of  separate  windings  or  by  special  connections  of  the 
series  fields,  it  may  be  possible  to  provide  this  feature  in  direct- 
current  equipments.  It  must  be  admitted,  however,  that  the 
use  of  coasting  will  reduce  by  a  considerable  amount  the  advan- 
tage to  be  gained  by  regeneration. 


SYSTEMS  FOR  ELECTRIC  RAILWA  Y  OPERATION  359 

Three -Phase  System. — The  use  of  alternating  current  was 
introduced  in  Europe  about  15  years  ago,  the  distribution  being 
by  the  three-phase  system.  At  that  time  the  only  motor  which 
could  be  used  for  traction  on  such  a  circuit  was  the  polyphase 
induction  motor.  Although  other  types  of  polyphase  machines, 
employing  commutators,  have  been  developed  since  then,  none 
of  them  has  characteristics  which  would  be  suitable  for  rail- 
way service,  or  would  give  better  results  than  the  induction  type. 
Three-phase  distribution  may  be  said  to  call  for  the  use  of  the 
latter  as  a  necessity. 

The  induction  motor  is  one  of  the  most  rugged  machines  built. 
In  the  squirrel-cage  type,  the  secondary  is  a  compact  structure, 
not  connected  in  any  way  to  the  external  circuit,  so  that  no 
commutator  or  collector  is  required.  The  secondary  winding 
is  exceedingly  simple,  consisting  of  heavy  copper  bars  short-cir- 
cuited to  resistance  rings  at  the  ends  of  the  core.  The  primary 
winding  is  not  complicated,  being  comparable  to  that  of  a  direct- 
current  armature  without  the  commutator.  When  it  is  necessary 
to  employ  a  wound  secondary,  as  is  usually  the  case,  a  regular 
phase  winding  similar  to  that  on  the  primary  is  used,  and  the 
terminals  are  connected  to  a  short-circuiting  resistance  through 
collector  rings.  In  this  form  the  motor  is  slightly  more  compli- 
cated than  the  squirrel-cage  machine,  but  the  difference  is  small, 
and  the  simplicity  of  the  design  is  still  much  greater  than  that  of 
any  motor  using  a  commutator. 

The  induction  motor  is  probably  the  lightest  of  any  built  for 
railway  service,  and  is  correspondingly  cheap.  The  efficiency  is 
quite  high,  and  the  power  factor  may  be  made  satisfactory-  for 
commercial  purposes.  The  difference  in  performance  between 
the  induction  motor  and  the  direct-current  series  motor  is  slight; 
but  if  there  is  any  advantage,  it  is  on  the  side  of  the  alternating- 
current  machine. 

The  disadvantage  of  the  induction  motor  lies  in  the  fact  that 
it  is  a  constant-speed  machine.  Although  the  advocates  of  the 
three-phase  system  claim  that  constant  speeds  are  preferable,  rail- 
way operators  in  the  United  States  are  not  convinced  that  it 
would  be  desirable  to  change  from  the  variable  speed  which  has 
characterized  the  operation  by  steam  locomotives  for  nearly  a 
century.  On  the  other  hand,  it  may  be  argued  that  there  are  but 
a  few  speeds  available  with  direct-current  series  motors,  although 
these  few,  unlike  those  of  the  induction  motor,  are  not  constant 


360  THE  ELECTRIC  RAILWAY 

over  a  wide  range  of  load.  It  is  difficult  to  make  a  fair  decision 
between  the  two  methods,  for  the  data  at  hand  with  regard  to 
constant-speed  operation  of  large  railroad  systems  is  entirely 
inadequate  for  a  comparison. 

The  method  of  control  used  for  induction  motors  is  somewhat 
similar  to  that  for  direct-current  motors,  in  that  the  speed  is 
lowered  at  starting  by  the  use  of  resistance  in  the  motor  circuits. 
If  concatenation  of  motors,  or  other  means  to  give  a  reduced  run- 
ning speed,  be  used,  the  losses  in  the  control  resistors  are  not  much 
greater  than  when  direct-current  motors  are  operated  with  series- 
parallel  control.  In  many  ways  there  is  but  little  choice  between 
the  two.  The  alternating-current  control  has  one  marked  ad- 
vantage, in  that  the  potential  to  be  handled  is  low,  and  is  in  a 
local  circuit,  where  disarrangement  of  the  resistor  connections 
can  do  but  little  damage;  while  the  resistors  in  the  direct-current 
control  are  inserted  in  the  main  circuit  between  the  contact  line 
and  the  motors.  With  induction  motors  the  main  circuit  need 
not  be  opened  at  all  when  power  is  being  drawn  from  the  line, 
so  that  the  danger  from  arcing  at  the  controller  contacts  is  re- 
duced to  a  minimum. 

The  great  disadvantage  of  the  three-phase  system  is  the  com- 
plicated contact  line.  Using  the  track  rails  as  one  conductor, 
two  additional  lines  are  necessary,  so  that  two  parallel  trolley 
wires,  each  carrying  the  full  potential,  must  be  supported  above 
the  track.  The  greatest  difficulty  is  found  in  maintaining  the 
insulation  between  these  conductors.  This  is  especially  true 
where  there  are  many  turnouts,  crossovers,  and  other  special 
work,  since  the  wires  of  opposite  potential  must  be  insulated 
from  each  other.  These  difficulties  have  limited  the  pressure  in 
most  cases  to  about  3300  volts,  so  that  the  primary  purpose  of 
the  three-phase  distribution,  to  allow  a  high  working  potential,  is 
in  part  defeated.  Aside  from  this,  the  distribution  is  quite 
flexible,  since  the  e.m.f.  can  be  changed  by  stationary  transform- 
ers placed  along  the  track,  and,  if  the  motors  are  wound  for  lower 
pressures  than  the  trolley,  reducing  transformers  can  be  placed  on 
the  locomotives  and  cars. 

The  economy  of  the  distribution  system  is  quite  high,  for  in 
spite  of  the  fairly  low  potential,  there  is  a  considerable  saving  in 
loss  due  to  the  inherent  property  of  the  three-phase  circuit,  that 
three  conductors  give  the  same  loss  as  four  of  the  same  cross- 
section  in  the  two-phase  system,  or  two  of  double  section  in  the 


S  Y STEMS  FOR  ELECTRIC  RAILWA  Y  OPERA  TION  361 

single-phase  or  direct-current  systems,  for  the  same  effective 
pressure. 

With  the  three-phase  system,  using  induction  motors,  regenera- 
tion of  energy  on  down  grades  can  be  obtained  automatically 
without  any  modification  of  the  control  circuits.  All  that  is  re- 
quired is  to  leave  the  motors  connected  to  the  line.  This  is 
especially  useful  when  heavy  freight  trains  must  be  handled  on 
long  down  grades,  in  which  case  the  control  of  the  train  without 
the  use  of  brakes  is  safer,  and  gives  considerable  saving  in  brake- 
shoe  wear. 

The  Single-Phase  Alternating-Current  System. — This  is  much 
more  flexible  than  the  three-phase  system  in  the  range  of  equip- 
ment which  can  be  applied.  Most  of  the  installations  up  to  the 
present  time  have  used  machines  of  the  commutator  types,  with 
characteristics  nearly  the  same  as  those  of  the  direct-current 
series  motor.  While  these  are  quite  satisfactory  from  an  operat- 
ing standpoint,  they  are  considerably  more  complicated,  are  from 
10  to  20  per  cent,  heavier  for  the  same  output,  and  correspond- 
ingly more  expensive  than  direct-current  series  motors  of  the 
same  rating.  This  disadvantage  is  partially  overcome  by  oper- 
ating the  single-phase  machines  at  higher  speeds,  although  this 
has  in  itself  some  objections.  Single-phase  commutator  motors 
have  full-load  efficiencies  from  one  to  two  per  cent,  lower  at  full 
load  than  direct-current  motors. 

By  the  use  of  a  "  phase-splitter, "  three-phase  induction  motors 
may  be  operated  on  the  single-phase  distribution  circuit,  thus 
giving  a  performance  identical  with  that  of  the  three-phase  sys- 
tem. In  some  cases  the  use  of  this  combination  may  be  justified; 
and  it  is  actually  being  applied  in  one  instance  in  America. 

If  the  mercury  vapor  rectifier  fulfills  the  present  expectations, 
it  will  make  the  single-phase  circuit  available  for  use  in  connec- 
tion with  a  suitable  type  of  direct-current  motor,  giving  any 
required  range  of  characteristics. 

The  control  of  single-phase  series  motors,  or  of  direct-current 
motors  through  a  rectifier,  is  quite  simple,  and  is  much  more  effi- 
cient than  the  series-parallel  control  used  with  direct-current  cir- 
cuits. If  three-phase  motors  are  employed,  the  control  must  be 
effected  with  resistance  alone,  or  in  combination  with  concatena- 
tion or  pole-changing  connections,  in  which  case  the  efficiency  is 
about  the  same  as  for  the  direct-current  system. 

The  single-phase  contact  line  is  simple,  and  in  this  respect  is 


362  THE  ELECTRIC  RAILWAY 

on  a  par  with  direct  current.  The  principal  argument  in  favor 
of  the  single-phase  system  is  in  the  high  tension  which  can  be  used 
effectively  on  the  contact  line;  and  it  is  in  this  respect  that  it  is 
ahead  of  all  the  other  methods.  With  the  aid  of  lowering  trans- 
formers on  the  cars  or  locomotives,  the  motors  can  be  wound  for 
any  suitable  pressure,  irrespective  of  the  distribution  potential. 
There  has  been  no  serious  difficulty  in  maintaining  good  insulation 
of  the  contact  line  at  pressures  as  high  as  20,000  volts.  This  high 
potential  reduces  the  current  to  a  point  where  the  conductor 
section  can  be  very  small;  in  fact,  the  size  of  the  trolley  wire  for 
mechanical  strength  is  in  practically  every  case  great  enough  that 
no  supplementary  feeders  are  necessary,  even  for  heavy  traffic. 

The  distribution  circuit  as  a  whole  is  the  simplest  in  character 
of  that  for  any  system,  and  the  converting  equipment  consists 
only  of  single-phase  transformers  of  the  proper  rating,  spaced 
along  the  track.  The  high  distribution  potential  makes  possible 
the  use  of  long  distances  between  substations,  so  that  the  load- 
factor  is  improved  over  that  obtained  with  any  system  operating 
at  a  lower  pressure.  In  addition,  the  use  of  a  control  consisting 
of  taps  from  the  secondary  of  the  car  transformer  makes  the 
actual  value  of  the  potential  drop  of  very  little  importance,  and 
high  accelerating  current  or  high  speed  may  be  maintained  under 
practically  all  conditions. 

Rotating  machinery  is  required  in  the  distributing  circuit  only 
when  it  is  necessary  to  change  the  frequency;  and,  as  satisfactory 
motors  can  be  designed  for  25  cycles,  there  is  little  difficulty  in 
using  standard  apparatus,  without  frequency  changers.  If  it  is 
found  desirable  to  generally  adopt  motors  designed  for  operation 
on  a  frequency  of  15  cycles,  either  a  separate  generating  and 
distributing  system  must  be  provided,  or  else  rotating  frequency 
changers  must  be  used.  But  the  recent  developments,  men- 
tioned in  the  preceding  paragraphs,  in  the  use  of  different  types 
of  motors  on  the  single-phase  contact  line  may  make  such  an 
arrangement  unnecessary.  With  the  use  of  the  rectifier,  it  would 
even  be  possible  to  operate  the  system  at  the  commercial  fre- 
quency of  60  cycles. 

So  far  as  can  be  determined,  there  is  no  danger  of  electrolysis  with 
alternating  current,  although  this  advantage  is  slight,  since  the 
single-phase  system  is  best  suited  to  cross-country  work,  where 
the  danger  to  other  metallic  structures  in  the  surrounding  earth  is 
a  minimum. 


S  Y 'STEMS  FOR  ELECTRIC  RAILWA  Y  OPERA  TION  363 

If  induction  motors  are  used,  regeneration  of  electric  energy  is 
automatic;  but  while  it  is  easily  possible  to  recover  energy  with 
single-phase  commutator  motors,  it  is  questionable  whether  the 
complication  in  the  control  would  not  offset  the  advantages  to  be 
gained. 

Field  of  the  Systems. — Up  to  the  present  time,  the  use  for  city 
service  of  the  600-volt,  direct-current  system  is  universal  in 
America,  and  practically  so  all  over  the  world.  While  this  may  be 
due  largely  to  its  early  application  in  all  important  installations, 
there  is  no  conclusive  argument  to  be  made  against  it.  The 
series  motor  has  the  characteristics  required  for  rapid  accelera- 
tion; and,  although  the  direct-current  control  is  somewhat  ineffi- 
cient, the  loss  due  to  the  extra  weight  of  apparatus  for  single- 
phase  operation  leaves  a  wide  margin  in  favor  of  the  former.  The 
use  of  the  low-tension  distributing  circuit  is  to  some  extent  a 
disadvantage,  but  the  distances  through  which  the  direct  current 
must  be  transmitted  are  relatively  quite  short,  so  that  the  total 
loss  is  not  excessive.  One  of  the  worst  features  incident  to  direct 
current  in  city  service  is  the  necessity  for  locating  substations  at 
central  points  where  the  cost  of  real  estate  is  high.  Another 
disadvantage  is  the  danger  of  damage  from  electrolysis.  This 
latter  trouble  can  be  overcome  to  a  great  extent  by  the  proper 
maintenance  of  the  return  circuit,  and  it  is  seldom  necessary  to 
resort  to  the  heroic  remedy  of  using  two  trolley  wires. 

For  suburban  and  interurban  service,  where  a  portion  of  the 
run  must  be  made  over  city  streets,  a  combination  system  which 
will  allow  the  same  motors  to  be  used  for  all  parts  of  the  road  is 
desirable.  The  earlier  lines  of  this  class  are  all  equipped  with 
the  600-volt  system,  as  it  was  the  only  one  available  at  the  time 
they  were  installed.  A  few  roads,  built  about  ten  years  ago,  were 
equipped  with  single-phase  series  motors,  with  a  duplicate  control 
so  arranged  that  they  could  run  either  on  alternating  or  direct 
current.  In  practically  every  case  such  operation  has  been  to  a 
large  degree  unsuccessful,  mainly  on  account  of  the  great  com- 
plication and  excessive  weight  of  the  equipment.  For  this  class 
of  service  the  use  of  1200  volts  direct  current  has  been  a  more 
satisfactory  solution  of  the  power  supply  problem,  since  the 
added  complication  to  adapt  the  motors  and  control  for  both 
circuits  is  comparatively  small.  A  large  number  of  roads,  for- 
merly using  600  volts,  have  rearranged  their  distribution  circuits 
to  admit  of  1200-volt  operation,  with  satisfactory  results. 


364  THE  ELECTRIC  RAILWAY 

For  heavy  service,  any  of  the  systems  are  available,  and  all  of 
them  are  used.  There  is  no  general  agreement  as  to  which  is  the 
best  suited  for  all-around  railroad  work;  but  it  is  quite  evident 
that  for  long-distance  lines  a  high-tension  distribution  circuit  is  a 
prime  necessity.  This  of  course  rules  out  the  600-volt  system 
from  consideration  for  such  roads,  although  where  it  has  been 
installed  for  terminal  service,  it  has  in  all  cases  given  good 
satisfaction.  In  America,  the  choice  seems  to  lie  between  the 
single-phase  and  high-tension  direct  current.  Developments  are 
taking  place  so  rapidly  at  the  present  time  that  it  is  impossible 
to  predict  that  one  or  the  other  system  will  prove  greatly  supe- 
rior. There  is  no  immediate  prospect  of  the  use  of  direct  poten- 
tials comparable  with  those  for  single-phase  circuits;  but  the 
lower  distribution  losses  incident  to  direct  current  put  it  more 
nearly  on  a  par  with  its  competitor  than  it  otherwise  would  be 
Three-phase  distribution  has  not  been  a  serious  factor  in  this 
country,  although  it  has  been  very  successful  abroad  in  several 
important  installations.  In  view  of  recent  developments,  it  is 
doubtful  whether  the  straight  three-phase  system  with  induction 
motors  will  meet  the  needs  of  American  railroads. 

Single-phase  operation  has  the  greatest  possibilities  for  heavy 
service.  The  ability  to  use  any  known  type  of  propulsion  motor, 
with  the  converting  equipment  on  the  locomotive,  makes  it  as  near 
a  universal  system  as  can  be  obtained.  Even  if  some  roads  should 
adopt  other  methods  of  distribution,  it  is  still  possible  to  design 
single-phase  locomotives  so  that  they  can  be  run  efficiently  on 
such  circuits.  With  induction  motors,  the  same  locomotive 
could  be  operated  on  three-phase  circuits  with  a  comparatively 
slight  complication  of  the  control;  and  the  same  is  true  of  direct- 
current  motors  if  used  on  the  single-phase  circuit  through  some 
form  of  converter.  Recent  developments  make  it  seem  doubtful 
whether  the  alternating-current  commutator  motor  will  survive, 
at  least  in  its  present  form;  but  the  use  of  this  machine  is  only 
an  incident  to  the  successful  development  of  the  single-phase 
system. 


CHAPTER  XVIII 
ENGINEERING  PRELIMINARIES 

Electric  Railway  Location. — The  proper  location  of  an  electric 
rail  way  is  a  problem  involving  a  considerable  number  of  variables, 
all  of  which  must  be  given  consideration  if  the  best  possible  result 
is  to  be  obtained.  The  quantities  entering  are  so  numerous  and 
so  diverse  that  it  is  almost  impossible  to  determine  absolutely  in 
all  cases  the  best  location,  equipment  and  schedule.  The  last 
quantity  is  one  which  can  be  modified  at  will,  within  the  limits  of 
the  rolling  stock  and  the  electric  system;  but  the  first  two,  when 
once  chosen,  are  quite  difficult  to  modify  without  incurring  a 
large  additional  cost.  It  is,  therefore,  exceedingly  important 
that  the  preliminary  engineering  be  very  carefully  done,  since  the 
final  success  of  a  road  may  be  seriously  jeopardized  if  mistakes 
are  made  at  this  point. 

City  Roads. — The  requirements  of  nearly  all  cities  of  large  or 
moderate  size  for  purely  urban  transportation  have  been  largely 
met  at  the  present  time,  so  that  a  study  of  the  requirements  for 
such  lines  is  almost  entirely  academic.  The  method  of  deter- 
mining the  proper  equipment  is  of  some  value,  as  it  gives  a 
means  of  checking  existing  installations  as  to  their  adequacy.  In 
some  cases,  where  the  present  facilities  are  insufficient,  such  a 
study  may  lead  to  the  extension  of  the  lines  to  meet  the  needs  of 
the  inhabitants. 

The  length  of  track  which  a  city  can  support  is,  to  a  large 
extent,  a  function  of  the  population.  The  relation  of  population 
to  length  of  track  per  thousand  inhabitants  for  a  number  of 
American  cities  is  shown  in  Fig.  192.  It  will  be  seen  that  the 
proportional  length  of  track  which  a  city  can  support  decreases  as 
the  density  of  population  increases  up  to  a  certain  point,  after 
which  it  becomes  sensibly  constant.  This  would  be  expected, 
since  the  smaller  cities,  in  order  to  give  any  kind  of  service,  must 
provide  relatively  large  amounts  of  track,  even  though  the  num- 
ber of  passengers  carried  is  comparatively  small.  As  the  size  of 
cities  increases,  the  use  which  is  made  of  the  existing  track  is 

365 


366 


THE  ELECTRIC  RAILWAY 


greater,  so  that  the  additional  amount  of  line  which  has  to  be 
installed  per  inhabitant  becomes  decidedly  less  in  the  larger 
urban  centers.  A  saturation  point  is  finally  reached,  beyond 
which  the  increase  in  necessary  track  is  practically  in  proportion 
to  the  population.  The  place  where  this  condition  occurs  de- 
pends largely  on  the  compactness  of  the  city  and  the  number  of 
independent  centers  which  exist  within  the  community.  The 
more  concentrated  the  population,  the  less  is  the  ultimate  limit 
for  the  amount  of  track  per  inhabitant. 


Boston 


^Portland, 


Ore. 


Manta 


<  )?rovidence 


^Washing-fan^ 


Jersey  City 


-Newark 


•neapolis-Sf-.Haul     st.lou 


ltimore 


OIZ34567& 

Population  in  Hundreds  of  Thousands. 
FIG.  192. — Relation  of  urban  track  to  population. 

In  some  cities  the  amount  of  track  which  can  be  used  is  much 
greater  than  the  average.  Boston,  for  instance,  has  a  much 
greater  length  per  inhabitant  than  any  other  American  city  of 
similar  size.  This  difference  is  more  apparent  than  real,  for  a 
large  population  in  the  immediate  vicinity  of  the  metropolitan 
district  is  served  by  the  same  system,  so  that  additional  facilities 
for  the  adjacent  cities  are  not  required.  The  extra  demand  for 
transportation  from  the  surrounding  suburbs  will  increase  the  use 
of  the  city  railway  tracks,  so  that  the  earnings  may  be  exceedingly 
high  when  a  line  is  located  in  such  a  center.  Another  cause  for 


ENGINEERING  PRELIMINARIES  367 

extensive  use  of  the  road  is  when  the  physical  location  of  the  city 
is  such  that  it  is  impossible  or  difficult  for  the  inhabitants  to  walk 
to  and  from  their  homes.  An  example  of  such  a  city  is  New  York, 
where  the  business  district  is  of  such  a  character  that  very  few 
persons  can  live  within  easy  walking  distance  of  any  point  in  it. 
For  this  reason,  an  adequate  transportation  system  must  be  pro- 
vided to  permit  the  further  development  of  the  city.  In  fact,  in 
New  York  the  growth  of  the  city  railroads  is  decidedly  behind  the 
increase  in  population,  so  that  the  existing  facilities  are  strained 
to  the  utmost.  Similar  conditions  exist  in  many  other  places, 
but  the  results  cannot  be  so  clearly  seen  as  in  the  former  city. 

Future  Requirements. — In  addition  to  determining  the  present 
need  for  railway  facilities,  it  is  necessary  to  make  some  provision 
for  future  growth,  if  the  requirements  of  the  city  are  to  be  served 
for  any  length  of  time.  In  certain  cases  it  is  possible  to  make  such 
provision  merely  by  the  extension  of  the  existing  tracks  farther 
into  the  suburbs,  as  these  develop;  while  in  others  the  growth  of 
the  urban  section  may  make  a  complete  rearrangement  of  the 
entire  road  necessary.  Careful  design  of  this  part  of  the  system 
may  add  considerably  to  the  growth  which  can  be  taken  care  of 
without  extending  the  existing  tracks.  In  a  number  of  the 
smaller  cities  it  has  been  customary  to  route  all  cars  past  a  central 
point,  such  as  an  important  street  intersection  or  a  civic  center. 
Although  this  practice  makes  the  transfer  of  passengers  simple 
while  the  traffic  is  light,  it  is  likely  to  cause  serious  congestion 
when  the  city  has  developed  to  a  larger  size.  In  some  places 
where  this  arrangement  has  been  used,  considerable  objection  by 
the  public  has  developed  to  the  re-routing  of  cars  on  different 
thoroughfares.  This  condition  can  only  be  overcome  by  careful 
publicity  work  on  the  part  of  the  railroad  company. 

It  is  impossible  to  make  an  accurate  estimate  of  the  future 
growth;  but  consideration  should  be  had  of  the  variable  condi- 
tions which  may  enter  to  change  the  final  result,  and  the  lines  laid 
out  in  such  a  way  as  to  make  them  of  the  greatest  present  use, 
while  later  they  may  be  extended  to  meet  the  future  needs.  Even 
at  the  present  time  such  precautions  may  be  taken  in  planning 
extensions  to  existing  lines,  and  in  this  way  the  improvements 
will  be  of  greater  value  to  the  community  than  if  changes  are 
made  to  meet  the  present  requirements  only. 

The  second  important  factor  in  determining  the  adequacy  of  a 
street  railway  is  the  use  made  of  it  by  the  public.  Again  statis- 


368 


THE  ELECTRIC  RAILWAY 


tics  may  be  employed  to  show  the  probable  value  of  a  road  to  a 
city.  The  number  of  rides  which  each  inhabitant  is  liable  to  take 
increases  with  the  size  of  the  place  in  which  the  road  is  located, 
the  growth  being  very  rapid  in  the  smaller  towns  and  much  less 
after  a  certain  size  is  reached.  A  curve  between  the  annual  num- 
ber of  rides  per  inhabitant  and  the  size  of  the  city  is  shown  in  Fig. 
193.  This  information  is  valuable  in  connection  with  estimates 
of  probable  growth  in  population  to  prevent  making  the  assump- 


600 


OIZ3456 

Population     in  Hundreds  of  Thousands. 

FIG.  193.  Relation  of  rides  per  inhabitant  to  population. 

tion  that  the  use  of  the  road  will  increase  as  a  direct  function  of 
this  gain. 

Since  the  rate  of  fare  in  most  cities  is  fixed  by  law,  the  values 
determined  above  give  at  once  the  gross  earnings  from  trans- 
portation. The  fare  on  practically  all  urban  lines  is  five  cents, 
so  the  number  of  passengers  is  a  direct  measure  of  the  receipts. 
It  should  be  noted  that  transfer  passengers  must  be  omitted 
from  this  estimate,  since  they  do  not  add  anything  to  the  revenue, 
although  it  is  the  usual  practice  to  include  them  in  the  total  num- 
ber of  passengers  carried.  On  this  point  there  is  a  great  deal  of 
misunderstanding,  since  many  railway  officials  look  on  transfers 


ENGINEERING  PRELIMINARIES  369 

as  an  unmitigated  evil.  This  is  largely  a  misapprehension,  for 
the  use  of  transfers  often  permits  the  routing  of  cars  to  give  a 
much  more  efficient  service  than  were  through  routes  used  exclu- 
sively. In  such  cases  the  use  of  transfers  is  a  positive  benefit  to 
the  company. 

Number  of  Cars. — The  number  of  cars  and  the  frequency  with 
which  they  are  operated  are  quite  difficult  to  estimate  properly. 
They  have  a  direct  effect  on  the  cost  of  the  service  and  an  indirect 
one  on  the  number  of  passengers  carried.  Other  things  being 
equal,  the  number  of  persons  who  will  ride  increases  with  the 
frequency  of  operation  up  to  the  point  where  cars  are  run  every 
two  or  three  minutes.  Beyond  this  there  is  no  great  possibility  of 
obtaining  more  passengers  in  this  way.  The  worst  feature  in 
modern  city  operation  comes  from  the  excessive  congestion  of 
traffic  at  certain  times  during  the  day.  By  far  the  greatest  num- 
ber of  the  regular  passengers  begin  work  at  approximately  the 
same  hour,  and  stop  at  the  same  time.  This  means  that  facilities 
for  handling  a  great  number  of  passengers  must  be  provided, 
while  they  are  only  in  use  for  a  few  hours,  twice  a  day.  Even 
with  the  best  and  most  modern  equipment,  it  is  hard  to  provide 
even  standing  room  for  all  the  passengers,  while  at  other  times  the 
cars  will  be  nearly  empty.  This  condition  is  inherent  to  Ameri- 
can business  methods,  and  can  be  avoided  only  by  a  large  amount 
of  educational  work.  A  variation  of  only  a  few  minutes  in  the 
time  for  closing  stores,  factories  and  offices  would  make  a  great 
reduction  in  the  peak  of  the  load,  with  a  corresponding  improve- 
ment in  the  service.  This  point  has  already  been  considered  in 
connection  with  the  determination  of  power  requirements. 

It  is  erroneous  to  suppose  that  the  greatest  earnings  of  the 
railways  come  from  the  crowded  cars  run  during  the  rush  hours. 
As  a  matter  of  fact,  the  congestion  calls  for  the  operation  of  cars 
additional  to  those  on  the  regular  schedule.  Although  these 
special  cars  are  used  but  a  few  hours  a  day,  their  first  cost,  and  the 
cost  of  the  entire  system  necessary  for  their  operation,  is  as  great 
as  though  they  were  in  continuous  service.  In  addition  the 
platform  men  must  be  given  a  living  wage,  and  this  must  be 
done  even  if  the  amount  of  time  of  actual  service  is  but  two  or 
three  hours  a  day.  It  is  not  often  possible  to  arrange  schedules 
to  provide  continuous  employment  for  these  men. 

Size  and  Type  of  Cars. — The  proper  determination  of  the  type 
of  car  to  use  for  any  urban  road  is  largely  a  matter  of  individual 

24 


370  THE  ELECTRIC  RAILWAY 

taste.  Many  kinds  are  in  use  on  such  lines,  and  the  apparent  lack 
of  agreement  indicates  that  no  single  type  is  entirely  satisfactory 
for  all  classes  of  service.  It  would  appear  that  for  street  railways 
in  the  smaller  cities,  cars  with  bodies  about  20  ft.  in  length, 
mounted  on  single  trucks  and  equipped  with  two  motors  of  from 
20  to  30  kw.  each,  will  meet  the  average  requirements.  Cars 
of  this  type  will  seat  about  twenty  passengers  and  will  provide 
standing  room  for  as  many  more.  For  the  larger  cities,  addi- 
tional capacity  must  be  provided,  which  can  be  done  only  by 
the  use  of  units  of  greater  size.  This  naturally  calls  for  double- 
truck  cars,  since  a  20-ft.  body  is  about  the  longest  which  can  be 
mounted  on  a  single  truck,  unless  some  form  of  non-parallel  axle 
is  used.  The  details  of  cars  for  this  class  of  service  have  been 
discussed  in  Chapter  VIII. 

Schedule  and  Maximum  Speeds. — In  many  cities,  the  maxi- 
mum speed  of  cars  is  defined  by  law.  While  this  has  some  effect 
on  the  schedule  speed,  it  can  be  offset  by  the  acceleration  which  is 
used.  It  has  been  shown  in  previous  chapters  that  the  latter 
has  as  great  an  effect  on  the  schedule  speed  in  short  runs  as  does 
the  maximum  velocity  attained.  When  a  great  many  stops  are 
made,  the  schedule  speed  which  can  be  reached  is  usually  very 
low,  often  not  more  than  10  miles  per  hr.,  unless  the  motor 
equipment  is  entirely  abnormal.  It  is  advisable  not  to  attempt 
high  speeds  under  such  conditions,  since  the  cost  is  out  of  all 
proportion  to  the  advantage  gained. 

Where  the  run  includes  a  certain  distance  in  suburban  territory, 
in  which  the  speed  can  be  materially  increased,  it  is  frequently 
the  custom,  as  has  already  been  mentioned,  to  use  motors  for  the 
entire  division  geared  so  that  the  cars  may  operate  at  high  maxi- 
mum speeds  in  the  suburban  district.  The  result  of  this  is  to 
overload  the  motors,  while  the  schedule  speed  which  can  be  main- 
tained is  frequently  less  than  could  be  reached  were  the  same 
motors  used  with  a  higher  gear  ratio,  giving  a  lower  maximum 
speed.  The  most  desirable  arrangement  is  to  use  motors  geared 
for  the  maximum  acceleration,  but  obtaining  the  high  speeds 
needed  by  the  use  of  field  control.  This  will  give  the  advantages 
of  the  low  and  the  high  gear  ratios,  and  will  reduce  the  power  and 
energy  requirements  by  a  marked  degree.  Tests  which  have  been 
conducted  on  such  equipments  show  considerable  savings  over 
the  normal  single-speed  motors. 


ENGINEERING  PRELIMINARIES  371 

Interurban  Roads. — The  probable  earning  power  of  interurban 
railways  is  much  more  difficult  to  estimate  than  for  city  lines.  A 
great  deal  depends  on  the  kind  of  service  given  and  the  facilities 
which  are  offered  farmers  residing  along  the  road  for  light  freight 
service.  Generally,  high  schedule  speeds  are  less  important  than 
frequent  service,  since  a  large  part  of  the  passenger  traffic  is  local. 

Since  the  revenue  of  the  normal  interurban  railway  is  so  largely 
from  passenger  traffic,  a  careful  analysis  of  the  population  served, 
and  the  number  and  length  of  rides  per  inhabitant,  must  be  made 
in  order  to  get  a  close  estimate  of  the  probable  gross  earnings. 
The  factors  which  enter  are  so  materially  different  from  those 
which  govern  the  earnings  of  urban  roads  that  very  little  aid  can 
be  had  from  a  comparison  with  such  properties. 

The  sources  of  passenger  traffic  for  interurban  roads  depend  to  a 
large  extent  on  the  location  of  the  principal  cities  along  the  line. 
Usually  an  interurban  railway  is  constructed  with  one  city  of 
considerable  size  as  a  primary  terminal.  The  road  may  operate 
from  this  point  entirely  through  rural  territory,  serving  this  and 
the  small  towns  located  along  the  line;  or  it  may  connect  the  prin- 
cipal city  with  one  or  more  of  smaller  size.  The  greatest  source 
of  passenger  traffic  is  ordinarily  travel  from  the  rural  districts  to 
the  main  terminal;  but  if  the  road  exceeds  a  certain  length,  the 
traffic  from  this  source  will  not  increase  greatly  with  additional 
distance.  For  such  roads  a  second  terminal  is  necessary,  and  the 
greater  the  length  of  road,  the  more  intermediate  cities  are  essen- 
tial to  give  the  earnings  requisite  to  make  a  successful  property. 

The  estimation  of  the  city  population  served  is  apparently 
quite  simple;  but  to  obtain  figures  which  have  any  direct  value  is 
much  more  difficult.  The  travel  which  will  be  obtained  between  a 
terminal  city  and  the  surrounding  territory  does  not  depend  to 
any  material  extent  on  the  size  of  the  city,  but  rather  on  the  re- 
lations which  exist  between  the  urban  and  the  rural  populations. 
For  example,  a  county  seat  will  have  considerable  traffic  from 
the  surrounding  country,  but  very  little  to  it;  while  a  manufac- 
turing center  will  probably  develop  both  classes  of  travel,  espe- 
cially if  the  territory  surrounding  it  is  largely  of  the  same  general 
character. 

The  estimation  of  the  rural  population  served  by  the  proposed 
road  is  usually  made  by  considering  a  section  of  territory  from 
one  to  four  miles  wide,  on  each  side  of  and  contiguous  to  the  track. 
Some  objection  may  be  found  to  this  method,  in  that  the  amount 


372  THE  ELECTRIC  RAILWAY 

of  travel  to  be  expected  depends  perhaps  more  on  the  size  and 
character  of  the  towns  along  the  line  than  on  the  farming  popula- 
tion served  by  the  road.  An  alternative  method  is  to  adopt  a  fac- 
tor for  use  in  connection  with  the  population  of  the  intermediate 
towns  located  along  the  line. 

A  very  important  consideration  is  that  of  the  probable  future 
growth  of  the  territory  served,  and  an  estimation  of  the  effect  this 
will  have  on  the  earnings  of  the  road.  A  good  interurban  service 
does,  without  question,  develop  the  country  through  which  it 
passes;  but  the  amount  of  such  growth  may  be  a  vital  factor  in 
determining  the  success  or  failure  of  the  property.  It  is  usually 
impossible  to  build  roads  before  the  population  is  great  enough  to 
allow  them  to  earn  operating  expenses,  although  in  the  past  many 
such  lines  have  been  built;  but,  if  the  probable  increase  in  revenue 
due  to  the  presence  of  the  road  is  sufficient,  it  may  pay  to  install 
it  before  the  traffic  is  enough  to  pay  dividends  on  the  stock. 
Such  a  determination  is  very  difficult  to  make,  and  great  care 
should  be  taken  to  prevent  loss  of  capital.  In  general,  the  prob- 
able earnings  from  a  projected  line  are  subject  to  so  many  vari- 
ables that  the  best  procedure  in  such  preliminary  estimating  is  to 
secure  the  services  of  the  best  engineering  talent  available. 

Operating  Expenses. — Of  equal  importance  to  the  expected 
revenue  is  the  probable  expense  of  operation  of  the  road.  The 
principal  items  under  this  classification  are  maintenance  of  way, 
maintenance  of  equipment,  and  expenses  directly  concerned  in 
conducting  transportation.  Maintenance  charges  depend  to  a 
very  considerable  extent  on  the  excellence  of  the  construction 
and  the  equipment;  but  if  these  are  assumed  to  be  at  least  of 
average  quality,  the  estimation  of  maintenance  costs  can  be  made 
with  a  fair  degree  of  accuracy  by  comparison  with  existing  roads 
of  the  same  general  character. 

The  cost  of  conducting  transportation  is  a  function  of  the 
amount  of  service  given,  although  not  directly  dependent  on  it. 
The  cost  of  operating  a  car-mile  or  a  ton-mile  depends  very  largely 
on  the  number  of  such  units  hauled,  although  such  items  as  the 
overhead  charges  for  production  of  power  and  platform  labor 
are  very  nearly  constant  regardless  of  the  use  which  is  made  of 
the  road.  If  the  line  is  to  be  successful,  the  regular  schedules 
must  be  maintained  whether  any  traffic  appears  or  not;  and  the 
cost  of  hauling  empty  trains  is  very  nearly  as  great  as  when  they 
are  loaded  to  their  maximum  capacity. 


ENGINEERING  PRELIMINARIES  373 

Estimation  of  Construction  Cost. — The  estimation  of  the  cost 
of  construction  is  not  difficult,  once  the  components  have  been 
correctly  determined.  Having  the  power  demands,  the  capacity 
of  the  generating  and  substations  may  be  found  at  once,  the  num- 
ber of  units  being  selected  to  give  the  desired  subdivision  of  load, 
with  a  proper  number  of  reserve  machines.  By  the  application 
of  the  principles  of  transmission  and  distribution  circuits,  the 
proper  size  of  the  conductors  may  be  determined. 

The  methods  of  estimating  the  number  of  cars  are  various,  but 
if  a  certain  standard  of  service  has  been  decided  on,  as,  for  ex- 
ample, the  operation  of  one  train  in  each  direction  per  hour,  the 
required  number  may  be  found  at  once  from  an  inspection  of  the 
graphical  time-table.  A  certain  allowance  must  be  made  for 
extra  service,  for  repairs,  etc.  Generally  it  is  best  to  purchase  at 
the  beginning  the  minimum  number  which  will  give  the  desired 
service,  and  add  to  them  as  the  traffic  develops  and  the  use  of 
additional  cars  becomes  necessary.  In  this  way  the  latest  im- 
provements in  design  may  be  taken  advantage  of. 

The  methods  of  estimating  the  probable  amount  of  power  re- 
quired have  been  taken  up  in  the  preceding  chapters.  Once 
the  schedule  is  determined,  the  proper  speed-time  curves  to  give 
the  desired  performance  may  be  laid  out,  and  the  motors  selected 
to  meet  this  requirement.  From  the  current-time  and  potential 
curves,  the  power  demands  on  the  substations- and  on  the  gen- 
erating station  may  be  determined. 

The  amount  of  energy  needed  for  the  operation  of  the  desired 
schedule  is  found  at  once  by  an  integration  of  the  power-time 
curve;  and  if  the  efficiency  of  the  various  elements  of  the  equip- 
ment be  known,  the  output  of  the  generators  at  the  bus 
bars  and  the  quantity  of  coal  to  be  burned  on  the  grates  can  be 
calculated. 

The  cost  of  platform  labor  can  be  found  at  once  from  the 
number  of  car-hours  operated,  if  the  average  wage  has  been 
established.  Other  labor  is  more  difficult  to  determine,  depend- 
ing as  it  does  on  a  variety  of  factors.  The  number  of  power- 
plant  operators,  repair  shop  men,  and  similar  employees  is 
largely  independent  of  the  size  of  the  road,  until  it  reaches  con- 
siderable proportions.  The  office  force  required  to  handle  the 
business  is  quite  variable,  and  depends  not  so  much  on  the 
number  of  units  operated  as  on  the  individual  ideas  of  the 
management. 


374  THE  ELECTRIC  RAILWAY 

Having  determined  the  various  items  which  enter  into  the 
operating  cost,  the  total  may  now  be  found  as  their  sum. 

Net  Receipts. — The  difference  between  the  gross  receipts  and 
the  operating  expense  gives  the  net  income.  If  the  operating 
expense  is  found  to  be  greater  than  the  receipts,  the  investigation 
may  properly  end  at  this  point,  unless  it  is  found  possible  in  some 
way  to  predict  an  increase  of  the  one  or  a  reduction  in  the  other. 
If  the  estimate  indicates  a  net  return,  further  study  will  show 
whether  this  income  is  sufficient  to  pay  taxes,  fixed  charges,  and 
other  legitimate  overhead  costs,  and  after  doing  this  leave  a 
balance  available  for  dividends.  This  is,  of  course,  the  final 
measure  of  success  or  failure  of  a  road.  It  is  essential  that  the 
greatest  care  be  taken  to  make  the  preliminary  estimate  accurate, 
especially  if  any  doubt  exists  as  to  the  ability  of  the  projected  line 
to  pay  dividends;  and  it  is  better  to  leave  alone  a  project  rather 
than  run  the  risk  of  sustaining  material  loss. 

Steam  Road  Electrification. — A  type  of  problem  which  is 
becoming  of  increasing  importance  is  the  electrification  of  trunk 
lines.  Such  roads  are  usually  old  and  well-established  properties, 
which  have  already  developed  a  good  traffic.  The  problem  is 
here  much  simpler,  since  the  preliminary  determinations  of 
traffic  and  equipment  are  wholly  or  partially  solved  before 
beginning  the  estimates. 

In  many  cases,  all  that  is  desired  is  to  replace  the  existing  steam 
locomotives  with  electric,  keeping  substantially  the  same  sched- 
ules and  train  weights.  This  is  the  simplest  statement  of  the 
problem,  and  requires  the  least  preliminary  engineering.  Once 
the  system  for  the  contact  line  has  been  decided  on,  the  size  and 
equipment  of  the  locomotives  is  comparatively  easy  to  determine, 
since  they  will  be  of  the  same  rating  as  the  steam  engines  they 
replace.  Having  found  the  locomotive  capacity,  the  motor  char- 
acteristics must  next  be  selected  to  give  correct  operation.  The 
speed-time  and  power  and  energy  curves  may  now  be  drawn, 
giving  the  demand  on  the  substations  and  on  the  power  plant. 
The  equipment  for  these  parts  of  the  system,  and  for  the  trans- 
mission and  distribution  circuits,  may  be  selected,  and  the  total 
operating  cost  peculiar  to  the  electric  installation  found. 

The  criterion  of  excellence  which  must  be  met  is  that  the  oper- 
ating cost  of  the  electric  equipment  must  be  less  than  that  for 
steam,  after  including  a  proper  allowance  for  the  increased  cost  of 
construction.  If  the  total  annual  cost  is  less  than  for  steam  op- 


ENGINEERING  PRELIMINARIES  375 

eration,  the  project  is  feasible  and  may  be  recommended;  other- 
wise it  is  necessary  to  look  toward  other  reasons  for  the  adoption 
of  electricity. 

Even  though  the  electric  operation  of  a  division  may  not  show 
a  decreased  cost  directly,  there  may  be  other  conditions  which 
modify  the  problem  to  make  electrification  desirable.  It  may  be 
possible  to  haul  trains  at  a  higher  speed,  thus  permitting  the  pas- 
sage of  a  greater  number  of  tons  in  a  given  time;  or  it  may  be 
possible  to  give  more  frequent  passenger  service  by  operating 
more  and  lighter  trains.  Many  such  considerations  must  be 
looked  into  and  may  give  excellent  reasons  for  electrification, 
even  though  the  direct  saving  to  be  obtained  is  small. 

In  some  cases,  the  change  from  steam  to  electric  operation  has 
caused  an  increase  in  passenger  receipts.  This  is  sometimes  due  to 
the  fact  that  competing  lines  have  been  taking  a  large  share  of  the 
traffic,  which  can  be  regained  by  better  service;  and  in  other  cases 
to  an  increased  desire  to  travel,  on  account  of  the  improved 
accommodations.  It  is  impossible  to  do  more  than  hint  at  the 
possibilities  of  this  sort,  and  they  must  be  determined  for  each 
individual  case. 

An  instance  of  the  successful  application  of  electricity  is  in 
mountain-grade  operation.  Here  the  limiting  conditions  usually 
depend  on  the  weight  of  trains  which  can  be  handled  by  steam 
locomotives.  Some  roads  have  found  the  capacity  of  an  entire 
railway  system  limited  by  that  of  a  single  short  division.  If 
light  trains  are  run,  the  requirements  of  safe  operation  limit 
materially  the  capacity  of  the  track;  and  if  long  trains  are  used, 
the  speeds  which  are  feasible  with  steam  are  decidedly  low.  Elec- 
tric operation  makes  possible  the  running  of  heavy  trains  at 
fairly  high  speeds,  so  that  the  number  of  tons  which  can  be 
hauled  may  be  materially  increased.  This  is  due  to  the  prac- 
ticability of  concentrating  larger  amounts  of  power  in  the  equip- 
ment than  can  be  done  with  steam. 

Choice  of  System. — Reference  to  Chapter  XVII  will  show  that 
of  the  three  systems  of  secondary  distribution,  any  one  will  fulfill 
the  requirements  of  ordinary  trunk-line  operation.  No  general 
agreement  has  been  reached  as  to  the  complete  superiority  of  any 
one;  but  for  a  particular  installation  there  may  be  a  solution  of  the 
motive-power  problem  which  will  be  the  most  satisfactory.  If 
any  doubt  exists,  the  best  way  is  to  prepare  separate  estimates 
based  on  the  use  of  each  of  the  three  systems,  obtaining  the 


376  THE  ELECTRIC  RAILWAY 

relative  costs  of  installation  and  operation.  Except  in  rare 
cases,  one  of  them  will  show  a  lower  total  operating  cost  than 
either  of  the  others;  and,  unless  there  are  separate  considerations 
to  be  met,  this  is  the  one  which  should  be  adopted. 

It  would  be  exceedingly  desirable  to  adopt  for  an  entire  rail- 
road system,  or  for  all  the  railroads  of  the  country,  a  single  uni- 
versal plan  for  electrification.  This  would  permit  standardiza- 
tion of  equipment,  and  would  reduce  the  cost  of  the  various 
parts  of  the  electrical  apparatus.  Until  this  is  done,  the  cost  of 
installations  for  electric  lines  will  be  considerably  higher  than  if 
such  standardization  is  brought  about.  It  would  be  a  poor 
policy,  however,  to  postpone  the  electrification  of  such  lines  as 
warrant  the  change  until  such  a  condition  has  been  realized; 
for,  with  the  systems  all  possessing  points  of  excellence,  any  one 
of  them  may  show  operating  economies  which  will  make  the  sav- 
ing sufficient  to  warrant  its  adoption,  even  with  the  possibility 
of  a  future  change  in  case  some  universal  or  superior  type  of 
equipment  is  adopted  later. 

In  the  final  analysis,  it  may  be  seen  that  the  use  of  electric 
power  presupposes  a  certain  traffic  density  before  it  becomes  a 
paying  investment,  so  that  the  lines  of  heavy  travel  are  certain 
to  be  electrified  first,  except  that  where  coal  is  expensive  and 
electricity  is  cheap  a  comparatively  light  traffic  may  make  the 
change  desirable.  Such  conditions  exist  in  the  Mountain  states, 
where  water  power  is  available;  and  at  the  present  time  at  least 
one  important  road  is  equipping  its  main  line  for  electric  opera- 
tion in  the  interest  of  economy,  there  being  no  other  basic  reason 
for  the  adoption  of  electricity.  Apart  from  such  special  installa- 
tions, it  is  quite  probable  that  the  Eastern  roads  will  be  the  first 
to  use  electric  power  for  the  operation  of  long  divisions,  since 
they  are  the  ones  which  will  receive  the  greatest  benefits  from  so 
doing. 


INDEX 


Accelerating  force 

for  rotating  parts 

total 

Acceleration,  chart  of . . 

curve 

effect  on  power  curve 

mechanics  of 

rotational 

units  of 

Accelerator  car 

Adhesion  coefficient 

Adjuster,  slack 

Advantages  of  motor  car  trains. 

of  series  motor 

Air  brakes — see  Brakes 

cylinders,  sizes 

compressed,  power  for 

compressors 

resistance 

Alternating-current  distribution 

electrolysis 

signals 

single-phase  system 

field  of 

three-phase  system 

field  of 

American  Electric  Railway  En- 
gineering Association . 

Standard  bearing 

car  wiring 

signal  aspects 

indications 

track  rails 

trolley  wire 

American  Institute  of  Electrical 

Engineers 132, 

Angle  of  inclination  for  brake 

beams 

Angular  acceleration 

Application    of    electric    loco- 
motive types 

Arch  roof  for  cars . . 


Arcing  in  controllers 97 

Armature  construction 73 

13  speeds 74 

14  winding    for     single-phase 

16                      motors 82 

40              modern 78 

33      Armstrong,  A.  H 23 

128      Armstrong's  equation 23 

13  Arrangement     of     drivers     on 

14  electric  locomotives. .  .  249 
14              on  steam  locomotives 243 

208      Articulated  cars 204 

166      Atkinson  repulsion  motor 64 

187      Automatic  air  brake 190 

240              block  signals 341 

48              control 101 

189              slack  adjuster '. 187 

181              stop 352 

157              train  control 353 

189      Auxiliary  equipment,  car 220 

20              effect  of  frequency  on 62 

321               energy  for 157 

301      Average  motor  potential 140 

345 

361  B 

364 

359      Banking  of  curves — see  Super- 

363                      elevation    30 

Battery,  storage,  in  substations.  316 

Bearing  friction  of  d.c.  motor  .  .  57 

18              car 18 

224              motor 79 

338      Block  signals,  automatic 341 

337              telegraphic 341 

262      Blow-out,  use  of 95 

287      Bobtail  cars 201 

Bolsters,  truck 232 

141      Bond,  rail,  Chicago  type 293 

electric  welded 294 

180                inductive 347 

14                protected 294 

resistance  of 295 

246                soldered 294 

206      Bonding,  track 293 

377 


378 


INDEX 


Boosters,  use  of 277 

Bow  trolley 227 

Bracket  construction 285 

Brakes,  air 189 

automatic 190 

combined    straight    and 

automatic 195 

electropneumatic 192 

high-speed 192 

quick  action 191 

straight 190 

tests  of 193 

Brake   beams,    angle    of   incli- 
nation    181 

cylinders,  sizes 181 

electric 195 

emergency 196 

hand 187 

magnetic 195 

magnetic,  Newell 197 

momentum 199 

power,  need  for 165 

rigging 181 

calculation  of 184 

foundation 183 

truck 182 

shoe  wear,  effect  of  regen- 
eration on 161 

vacuum 195 

Braking 164 

curve 34 

forces,   distribution   of   on 

car 172 

rotational  inertia 179 

total 180 

transmission  of 172 

importance  of 164 

methods  available 164 

phenomena,  nature  of 166 

Brazed  bonds 294 

Bridge  connection 102 

for  supporting  contact  line .   286 

Brush  rigging,  development  of . .     73 

loss . .  58 


Cab  signals 351 

California  type  cars 204 


Capacity,    motor 131,  143 

substation 132 

Car,  cars 200 

accelerator 208 

articulated 204 

auxiliary  equipment  of ....  220 

bearings 17 

bobtail 201 

braking — see  Braking 164 

California  type 204 

center  door 208,  213 

classification 200 

structural 201 

collectors 225 

construction 204 

framing 205 

materials  of 204 

roof  framing 206 

convertible 203 

development 201 

door  arrangement 207 

double-truck 204 

electric 201 

elevated 214 

equipment,     miscellaneous  230 

fare  collection 210 

framing 205 

freight 219 

gasoline 255 

heaters 222 

electric 223 

hot  air 222 

hot  water 222 

stove 222 

heating 222 

power  for 158 

horse 201 

interurban 218 

lighting 220 

power  for 157 

-mile,  as  basis  for   energy 

consumption 151 

near  side 213 

number  of  for  city  system .  369 

one  man 214 

open 202 

painting 229 

parlor 219 

P-A-Y-E..                211 


INDEX 


379 


Car,  pay-within 212 

prepayment 211 

rapid  transit 214 

seating   arrangement ..  209,  218 

self-propelled 254 

comparison 259 

gas-electric 256 

gasoline 255 

storage  battery 257 

semi-accelerator 208 

semi-convertible 203 

side  door 207,  209 

single-truck 230 

sleeping 220 

storage  battery 257 

street 201 

subway 214 

trucks — see  Trucks 230 

wiring 224 

Cascade  control 120 

Cast-iron  motor  frames 74 

welded  rail  joints 266 

Catenary,  equation  of 279 

suspension 282 

Center  door,  cars 208,  213 

Center    of   gravity   of    electric 

locomotives 247 

Changes  in  frequency 120 

in  poles 119 

Characteristics   of  motors — see 

Motors 42 

Choice  of  equipment 332 

of  locomotives 253 

of  potential 327 

Circuit,  distributing — see  Dis- 
tributing Circuit 270 

return — see  Return  Circuit  292 
transmission — see      Trans- 
mission     324 

City  railways 365 

substations 319 

Classes  of  distribution  systems    318 

Classification  of  cars 200 

of  electric  motors 42 

of  signals 335 

Coasting  curve 33 

Coefficient  of  adhesion. : 166 

of  friction 168 

Coils,  armature 78 


Collection  of  fares .  210 

Collectors,  current 225 

of  induction  motors 83 

Combination  systems  of  control  116 

Commutating  poles 77 

Commutation    in    single-phase 

motors 67 

Commutator  construction 78 

motors,  a.c. — see  Motors.     58 

Comparison  of  converters 315 

of  control  methods 91 

of  self-propelled  cars 259 

of  shunt  and  series  motors.  46 
Compensated  repulsion  motor. .  64 
Compensating  winding,  use  of .  .  59 
Compensation  of  a.c.  motors.  62 

of  brake  hangers 180 

of  curves 29 

Compound  motor 43 

Compounding    of   transmission 

circuit 328 

Compressed     air — see     Motive 

Powers,  Air  Brakes 
Compressors  for  air  brakes  ....    189 

Concatenation  control 120 

Conductive    compensation   for 

a.c.  series  motor 62 

Conductor,  contact 286 

position     in      prepayment 

cars 210 

use  of  rails  as 292 

Conduit  system 290 

Constant-current  system 42 

Constant-potential  system 42 

Construction,  car 204 

cost  of 373 

power  plant 332 

railway  motor '. 71 

track 261 

Contact  conductor,  size  of ....   286 

line 278 

construction 284 

forms  of 279 

methods  of  supporting  .  .    284 

requirements  of 278 

three-phase 360 

surface 292 

Contactors,  use  of 97 

in  multiple-unit  control..  .    101 


380 


INDEX 


Continuous  rating  of  motors.  .  142 

track  circuit  signals 343 

Control 84 

automatic 101 

calculations  for 104 

cascade 120 

changes        in        armature 

strength 87 

combined  a.c.  and  d.c 116 

concatenation 120 

Jones  type 104 

locomotive 252 

methods  of 84 

practical  combinations.  .  90 

multiple-unit 98 

Sprague  system 99 

Type  M 100 

unit  switch  type 101 

need  for 84 

permutator 124 

potential  variation 85 

proportioning  of  resistances  104 

railway  motor 84 

rectifier 125 

resistors 113 

rheostatic 90 

limitations  of 91 

principle 86 

series-parallel 94 

advantages  of 93 

comparison    with    rheo- 
static    91 

comparison 356,  357 

principle 85 

series,  series-parallel 94 

single-phase 115 

special  systems 123 

split-phase 122 

tandem 120 

three-phase 117 

comparison 360 

train,  automatic 353 

transformer 115 

unit-switch 101 

Ward  Leonard 123 

Controlled  manual  system 341 

Controller,  drum  type 95 

Jones  type 104 

operating Ill 


Controller,  pneumatically  oper- 
ated    103 

rheostatic 90 

type  HL 102 

typeK 95 

type  L 97 

type  M.... 100 

type  R 90 

Converters 307 

comparison  of 315 

mercury  vapor 312 

motor- 310 

synchronous 309 

types  of 307 

Convertible  cars 203 

Copper  loss  in  d.-c.  motor 57 

Corrosion  by  current 297 

natural 301 

Cost,  construction 373 

of  stops 153 

Counter  e.m.f 50 

Cradle  suspension 236 

Crecelius,  L.P 319 

Current,  heating  value  of 133 

limits  for  control 106 

rectified 314 

root  mean  square 134 

-squared  curve 136 

—time  curves 135 

Curves,  measurement  of 28 


D 


Defects  in  return  circuit 295 

Determination  of  train  resist- 
ance      22 

Development  of  car  design 201 

of  railway  motors 71 

of  substations 305 

Differential  coefficient 36 

Direct-current  circuit,  polarity 

of 300 

motors — see  Motors 42 

system,  field  of 363 

high-tension 357 

600-volt 355 

signals 342,  343 

Distant  signals 349 

Dispatching,  train 340 


INDEX 


381 


Distributing  circuit 270 

contact  line 278 

equations  of  272 

high-tension  d.c 303 

limiting  drop 273 

methods  of  feeding 275 

simple 271 

single-phase 304 

three-wire 302 

use  of  boosters 277 

use  of  graphical  time-table  273 

systems : 270 

classes  of 318 

complex 306 

d.c.,  comparison 357 

a.c.,  comparison 360,  362 

single-phase,  comparison.. .  362 
three-phase,  comparison. .  .  360 

Distribution,  a.c 321 

of  braking  forces  on  car.  .  .  172 

on  truck 174 

of  energy  consumption. ...  156 
systems,  electric 42 

Diversity  factor 333 

Doors,  car 207 

Double-rail  signals 346 

-trucks 232 

-truck  cars 204 

Drivers,  coupling  of 105 

speed  of 248 

Drop  in  distributing  circuit ....  272 
in  return  circuit . .  .  295 


E 


Early  motors 71 

Earnings,  net 374 

Earth  conduction 296 

Effect  of  potential  on  substation 

spacing 320 

Effective  current 134 

Efficiency  of  series  motor 58 

Electric  brakes 195 

cars 200 

distributing  circuit 270 

distribution  systems 42 

heaters 223 

locomotives — see  Locomo- 
tives..                           .  240 


Electric  motors — see  Motors. .  .  42 

railway  track — see  Track.  110 

systems,  advantages  of ....  9 

direct-current 8 

single-phase 8 

three-phase 8 

traction,  advantages  of  ...  11 

welded  bonds 294 

rail  joints 267 

Electrification,  scope  of 4 

steam  road 374 

Electrolysis 296 

alternating  currents  and .  .  301 

remedies  for 297 

Electropneumatic  brake 192 

Elevated  railway  cars 214 

Emergency  stops 194 

E.m.f .  method  of  speed  variation  50 

counter 50 

of  single-phase  motor 60 

Energy  consumption 147 

distribution  of 156 

effect  of  gear  ratio  on ...  151 

of  grades  on 155 

of  length  of  run  on    . .  153 

of  train  resistance  on  .  152 

for  auxiliaries 157 

methods  of  comparing  ..  151 

for  train  operation 147 

kinetic 148 

mechanical 12 

potential 12 

regeneration  of 158 

effects  on  equipment. . . .  161 

objections 162 

Engineering  preliminaries 365 

Equating  motor  load 133 

Equipment  of  locomotives 252 

power  plant,  choice  of  ....  332 

substation 316 

Estimation  of  construction  cost  373 

Expenses,  operating 372 


Fare  collection 210 

rate  of 368 

Feeding,  methods  of 275 

special  methods  of 302 


382 


INDEX 


Field  control  motors 144 

principle  of 87 

of  electric  locomotive 241 

of  railway  systems 363 

frames 74 

strength,  control  by 87 

variation  of 53 

weakening,  methods  of. ...  87 

Flange  friction 19 

Floating  bolster  trucks 232 

Flux  curve  of  series  motor 54 

Force  for  acceleration 13 

for  train  operation 38 

mechanics  of 12 

Forces,  braking — see  Braking.  .  172 

Forms  of  contact  line 279 

Formula,  train  resistance 23 

Foundation  brake  rigging 183 

Four-motor  equipments 145 

Frames,  motor 74 

Framing,  car 205 

Freight  train  resistance 25 

Frequency,  changes  in 89,  120 

changers,  use  of 362 

for  single-phase  motors  ...  61 

Friction 168 

effect  of  sliding  wheels.  ...  170 

flange 19 

journal 17 

of  motors  and  gears 21 

rolling 166 

sliding 168 

effect  of  variations  in ...  171 

of  distance  on 169 

of  pressure  on 170 

variation  with  speed. ...  168 

Functions  of  motive  powers  ...  42 
Future    requirements    for    city 

roads. .                         .  367 


Gas-electric  cars 256 

Gasoline  cars 255 

Gears,  choice  of 143 

friction  of 21 

motor 236 

ratio,  effect  on  energy  con- 
sumption   150 


Gears  ratio,  limits  to 238 

of  early  motors 74 

Generation,  power — see  Power.  330 

Generators,  efficiency  of 330 

subdivision  of 331 

Grades 26 

effect  on  energy  consump- 
tion   155 

ruling 28 

velocity 27 

virtual 27 

Graphical  time  table 273 

Grid  resistors 114 

Growth,  future,  of  population.  371 


Hand  brakes 187 

Head-end  resistance 20 

Heaters,  electric 223 

Heating,  car 222 

of  motors 131 

power  for 158 

value  of  current 133 

High-speed  brake , .  192 

-tension  d.c.  system 357 

transmission 326 

Horse  cars 201 

Horsepower  for  train  movement  41 

Hot  box,  cause  of 18 

Hydraulic  power 332 

Hysteresis  loss 58 


IR  drop,  effect  on  motor  speed  50 

in  distributing  circuit ....  272 

in  return  circuit 295 

PR  loss  in  series  motor 57 

Ice  load,  effect  on  trolley  wire .  .  282 

on  third  rail 289 

Incidental  resistances 26 

Inclination  of  brake  hangers.  .  .  180 

Indications,  signal 336 

Inductance      of      single-phase 

motor 59 

Induction  motor — see  Motors .  .  67 

-generator 307 

regulator  control 116 

series  motor .  .  63 


INDEX 


383 


Inductive  bonds 347 

Inertia,  rotational,  in  braking.  .  179 

Interlocking  signals 353 

Interpoles,  motor 77 

Interurban  cars 218 

railways 371 

substations 819 

Interval,  space 340 

Iron  loss  of  series  motor .  .  58 


Joints,    rail 263,  266 

Jones,  P.  N 104 

Journal  friction. .  17 


K 


Kelvin,   Lord 275,  318 

Kelvin's  law 275,  318 

Kilowatt  hours  per  car  mile. ...    151 
Kilowatts  for  train  movement.     41 

Kinds  of  signals 335 

Kinetic  energy 148 


Lamps,  car 220 

signals 336,  342 

Latour-Winter-Eichberg  motor.     64 
Length  of  run,  effect  on  energy 

consumption 153 

Leonard,  H.  Ward 123 

Leverage  in  brake  rigging 181 

Light  signals 336 

Lighting,  car 220 

power  for 157 

Limitations  of  rheostatic  control     91 
Lines,  transmission — see  Trans- 
mission     324 

Location  of  power  plant 331 

of  substations 318 

of  third  rail 288 

Locomotives,  electric 240 

applications  of 246 

center  of  gravity 247 

choice  of 253 

comparison  with  steam..  241 
control . .  .   252 


Locomotive,    electric,   coupling 

of  drivers 249 

development 240 

equipment 252 

field  of 241 

geared 244 

gearless 245 

interchangeability  of. ...  251 

motors 248 

motor  speeds 245 

number  of  drivers 249 

tractors 251 

types '.  243 

weight  on  drivers 250 

wheel  base 250 

gasoline 260 

special 260 

steam 6 

characteristics 6 

comparison  with  electric.  241 

development  of 1 

dirt  incident  to 7 

efficiency  of . . . 7 

types 243 

storage  battery 260 

wheel  classification 243 

Longitudinal  car  seats 209 

Losses  in  series  motor 56 

Lubrication  of  motors . .  79 


M 


Magnetic  brakes 195 

Magnetic  field  of  d.c.  motor.. .  .     54 

'Mailloux,  C.  0 35,  39,  133 

Manual  signal  systems 341 

Materials  for  car  construction. .   204 

Maximum  traction  trucks 233 

Mechanical     arrangements     of 

transmission   lines. .  .  .   329 

losses  of  d.c.  motor 57 

rectifier 315 

Mechanics,   fundamental  prin- 
ciples      12 

of  traction 12 

Mercury  vapor  rectifier.  .  .125,  312 
Methods    of   displaying    signal 

indications 336 

of  feeding 275 


384 


INDEX 


Methods    of    operating   sema- 
phores    348 

of  suspending  trolley  wire..  279 

of  train  spacing 339 

Momentum  brakes 199 

Monitor  roof 206 

Motion,  equations  of 31 

Motive  powers 6 

cable 2,  8 

compressed  air 7 

electricity 8 

functions  of 42 

gasoline 7 

steam  locomotive 6 

stored  steam 7 

Motor,  Motors 42 

a.c.  commutator 58 

induction 67 

induction  series 63 

power  required 146 

series 58 

conductively      c  o  in  - 

pensated 62 

inductively  c  o  m  p  e  n  - 

sated 63 

performance 65 

single-phase,  variation  of 

characteristics 66 

armature    construction 73 

speeds 74 

bearings 79 

capacity 131,  143 

-car  trains 240 

classification  of 42 

commutator  construction. .  78 

-compressors 189 

construction 71 

control. — see  Control 84 

-converter 310 

development 71 

d.c 42 

classification 42 

compound 43 

series 48 

comparison 355 

efficiency 58 

flux  curve 54 

losses 56 

for  regeneration 160 


Motor,  d.c.  series,  speed  char- 
acteristics   46 

variation  of 49 

torque  characteristic . .  53 

shunt 44 

for  regeneration 159 

early 71 

energy  consumption 150 

field  control 144 

for  traction 42 

frames 74 

friction 21 

gearing 74,    143,  236 

-generator,  induction  .  .  .  307 

sets 307 

synchronous 308 

heating  of 131 

induction 83 

comparison 359 

interpoles 77 

load,  character  of 132 

equating  of 133 

lubrication 80 

modern 75 

armatures 78 

number  of 144 

open  type 72 

polyphase  induction 67 

number  of  poles 69 

on  single-phase  circuit  . .  122 

performance  of 70 

speed  control 67 

potential,  average 140 

pressed  steel 75 

railway 10 

rating 132,  141 

repulsion 64 

Atkinson 64 

compensated 64 

selection  of 143 

series,  advantages  of 48 

single-phase 81 

commutation  of 67 

frequency  for 61 

sparking  in 60 

variations  of 62 

speeds  of 143 

calculation  of 50 

variation  with  resistance  52 


INDEX 


385 


Motor,  Sprague 

suspensions 

ventilation 

windings 

Multiple-unit  control 

N 


Near-side  car 

Net  receipts 

Newbury,  F.  D 

Newell  magnetic  brake . . . 
Nominal  rating  of  motors 

Nose  suspension 

Number  of  motors 


Oil  for  car  journals 

Open  cars 

Operating  expenses 

Operation  of  semaphores 

permissive 

systems  of 

time-interval 

Order,  train 

Oscillatory  resistance .... 

Overhead  trolley 

Over-running  third  rail . . 


Polar 


method 
current 


72      Polarity  of  d.-c.  circuit 300 

235      Poles,  changes  in 89,  119 

80  of  induction  motor 69 

78      Polyphase  induction  motor — see 

98  Motors 67 

system 359 

Population,  estimation  of 371 

relation  to  track 365 

213      Portable  substations 322 

374      Potential,  change  of 84 

319  effect  on  polyphase  induc- 

197  tion  motor 69 

141  on  substation  spacing.  .   320 

235  method  of  speed  variation .     51 

144  motor 140 

variation  of 85 

Power   factor   of   single   phase 

motors 59,     65 

19  for  a.-c.  motors 146 

202  for  train  movement 41 

372  generation 330 

348  requirements  of 330 

348  hydraulic 332 

355  plant,  capacity  of 330 

339  construction 332 

340  equipment,  choice  of ....  332 
19                  location 331 

279  purchased 333 

288  required  for  auxiliaries ....   157 

requirements 127 

—time  curves 130 

Preliminaries,  engineering. .....   365 

Preliminary  signals 349 

Prepayment  cars 211 

Pressures,  brake  shoe 177 

Preventive  coil,  use  of 116 

Protected  rail  bond 294 

Protection  from  electrolysis 297 

of  third  rail 288 

Pumps,  air 189 

Purchased  power 333 

Q 

Quick  action  brake 191 

R 

of     equating  Rail  bonding 293 

136  composition 263 


Painting,  car 229 

Pantograph  trolley 229 

Parabolic  equation  of  trolley 

wire 283 

Paving,  track 264 

Pay-as-you-enter  car 211 

Pay-within  car 212 

Performance,  motor — see  Motors  42 

Permissive  operation 348 

Permutator 312 

control 124 

Phase  splitter,  use  of 361 

Pinions,  motor 237 

Pipe  drainage  system 298 

Plotting  speed-time  curves ....  39 


386 


INDEX 


Rail  joints 263 

cast  weld 266 

cost  of  welding 269 

electric  weld 267 

special 266 

Thermit  weld 267 

welded 266 

reactance  of 295 

resistance  of 295 

sections 263 

signals 343 

third— see  Third  Rail 287 

track 262 

resistance  of 295 

Railway,  cable 2 

cost  of 3 

city 365 

adequacy  of 367 

future  requirements 367 

number  of  cars 369 

schedule  speeds 370 

size  of  cars 369 

type  of  cars 369 

'  use  of 367 

classification  of 5 

electric,  scope  of 4 

electrification 374 

interurban 3,  371 

motor  control 84 

problem 11 

street 2 

electric,  development  of.       3 

suburban 5,  370 

track— see  Track 261 

trunk  line 2 

Rapid-transit  cars 214 

Rating  of  motors 132,  141 

Reactance  of  rails 295 

Receipts,  net 374 

Reciprocal    method   for  speed- 
time  curves 39 

Rectifier,  efficiency  of 314 

mechanical 125,  315 

mercury   vapor 125,  312 

application  to  d.-c.  system  358 
application      to      single- 
phase  system 362 

Regeneration,  effects  on  equip- 
ment.. .    161 


Regeneration  of  energy 158 

with  d.-c.  system 358 

with  single-phase  system..   363 
with  three-phase  system .  .   361 
Regulation    of        transmission 

circuit 328 

Regulator,  induction 116 

Remedies  for  electrolysis 297 

Repulsion  motor — see  Motors.     64 
Requirements,  future,  for  city 

roads 367 

of  contact  line 278 

of  train  operation 127 

Resistance,  air 20 

control 86,     90 

effect  on  induction  motor. .     68 
for  controllers,  proportion- 
ing of 104 

incidental — see   Train   Re- 
sistance       26 

leads  in  single-phase  motor     61 

losses  of  d.c.  motor 57 

method  of  speed  variation     52 

of  return  circuit 295 

oscillatory 19 

rolling 19 

train-see  Train  Resistance     17 
used  for  weakening  motor 

field 88 

Resistors 113 

Retardation — see  Braking 164 

determination  of  correct.  .    171 

methods  for 164 

Retarding  force  for  braking. .  . .   180 

Return  circuit 292 

defects  in 295 

resistance  of 295 

use  of  rails  as 292 

Revenue  of  interurban  roads.  .   371 

Reverser,  controller 95 

Revolutions  of  drivers 248 

Rheostatic  control 90 

Richer,  C.  W 320 

Rigging,  brake 181 

Rigid  bolster  trucks 232 

Roads,  city 365 

Robinson,  Wm 344 

Rolling  friction 166 

resistance . .  19 


INDEX 


387 


Roof  framing  of  cars 206 

Root  mean  square  current 134 

Rotary  converter 309 

Rotational  acceleration 14 

inertia  in  braking 179 

Ruling  grade 28 

Run,  length  of,  effect  on  energy 

consumption 153 

Running  gear,  car 230 


S 


in  contact  wire 280 

effect  of  temperature  on. .  .  281 

method  of  calculation 280 

Saturation  of  magnetic  circuit.     45 
effect  of  speed   character- 
istic       47 

effect  on  torque  character- 
istic       45 

Schedule  speeds  for  city  rail- 
ways    370 

Schmidt,  E.  C 26 

Scofield,  E.  M 301 

Seating  arrangement  of  cars  . .  .   209 
Self-propelled  cars — see  Cars.  .   254 
Semaphores,  methods  of  operat- 
ing    348 

signals 336 

Semi-accelerator  car 208 

Semi-convertible  car 203 

Series  motor — see  Motors 48 

Series-parallel     c  o  n  t  r  o  1 — s  e  e 

Control 94 

Service  stops 194 

Shunt  motor — see  Motors 44 

Side  air  resistance 20 

-door  cars 208,  213 

friction 20 

Signals 335 

automatic  block 341 

cab 351 

car  counting 343 

controlled  manual 341 

for  a.-c.  roads 347 

for  d.-c.  roads 345 

for  operation  in  two  direc- 
tions     350 

indications 336,  337 


Signals,  interlocking. 353 

kinds  of 335 

light 337 

manual 341 

preliminary 349 

semaphore 336 

single-rail 345 

telegraphic 341 

track-circuit 343 

alternating  current 345 

double  rail  a.-c 346 

single  rail  a.-c 345 

trolley  contact 343 

uses  of 335 

wire  circuit 342 

Single-phase  motor  s — s  e  e 

Motors 58 

system 361 

transmission 325 

Single  rail  signal 345 

Size  of  contact  conductor 286 

Slack  adjuster 187 

Sliding  friction 168 

Soldered  rail  bonds 294 

Solid  frames  for  motors 75 

Space  interval 340 

Spacing  of  trains 339 

Span,  length  of 280 

wire  construction 285 

Sparking  of  single-phase  motor .     60 
Special  methods  of  feeding ....  302 

work,  track 269 

Speed  characteristics  of  motors     46 
control  by  field  weakening.     56 

of  induction  motor 68 

e.m.f .  of  single-phase  motor     60 
maximum,  effect  on  power 

consumption 127 

motor 49,  143 

of  a.c.  series  motor 65 

of  drivers 248 

schedule,  for  city  railways  370 

-time  curve 31 

acceleration  curve 33 

braking    curve 34,  194 

calculation  of 34 

coasting  curve 33 

components 33 

plotting 39 


388 


INDEX 


Speed-time,*  curve,  shunt   and 

series  motors... 48 

straight-line 128,    149 

with  electric  motors  ....    129 

Sperry,  E.  A 250 

Spikes,  track 262 

Split  frames  for  motors 75 

-phase  control 122 

Sprague,  F.  J 72,  99 

Station,    power — see  Power.  .  .   330 
Steam    locomotive — see    Loco- 
motive         6 

road  electrification 374 

Steel  motor  frames 74 

Stenger,  L.  A 301 

Stop,  automatic 352 

Stops,  cost  of 153 

Storage  battery  cars 257 

in  substations 316 

system  of  air  brakes 189 

Straight  air  brakes 190 

-line  speed- time  curves.. .  .    128 

Street  cars 201 

Substations. 305 

alternating-current 321 

capacity  of 318 

city 319 

development  of 305 

equipment 316 

interurban 319 

location  of 318 

portable 322 

spacing 320 

storage  battery  in 316 

Suburban  railways 370 

Subway  cars 214 

Suction,  rear 20 

Superelevation  of  outer  rail. ...     30 

Supports  for  trolley  wire 284 

Supporting  bridges  for  contact 

wire 286 

Surface  contact  system 292 

Suspension,  bracket 285 

by  bridges 286 

catenary 282 

motor 235 

span-wire 285 

Swinging  bolster  trucks 233 

Switches,  track 269 


Synchronous  converters 309 

motor-generator 307 

Systems,  distribution 42 

Systems,  electric — see    Electric 
for  electric  railway  opera- 
tion    355 

railway 355 

a.-c.  single-phase 361 

a.-c.  three-phase 359 

choice  of 375 

d.-c.  600-volt 355 

d.-c.  high-tension 357 

field  of 363 

three-phase 359 


Tandem  speed  control 120 

Telegraphic  block 341 

Temperature,  effect  on  sags  in 

wire 281 

Tension  in  trolley  wire 281 

Tests  of  air  brakes 193 

Thermit  weld 267. 

Third  rail 287 

collectors 229 

location  of 288 

over-running 288 

protection  of 289 

removal  of  ice 289 

resistance  of 290 

under-running 289 

Three-phase  control. 119 

motors — see  Motors 67,  83 

system 359 

transmission 325 

Thury   system 306,  325 

Ties,  track 261 

treated 262 

Time     element     in     controller 

operation Ill 

increment,  determination  of     34 

interval  operation 339 

-table,  graphical 273 

Ton-mile,  as  basis  for  energy 

consumption 151 

Torque  characteristic  of  motors.     44 

of  series  motor 53 

per  ampere 54 


INDEX 


389 


Track 261 

bonding 293 

-circuit  signals 343 

for  electric  railways 345 

construction 261 

in  paved  streets 264 

length  of,  relation  to  popu- 
lation    366 

rails 262 

reactance  of 295 

resistance  of . 295 

special  work 269 

ties 261 

Traction,  mechanics  of 12 

Tractive  effort 38 

of  single-phase  motor ...  65 

of  steam  locomotive.  .6,  10 

force,  calculation  of 38 

Tractors 251 

Traffic  of  city  roads 365 

of  interurban  roads 371 

Train  control 353 

movement,  power  for 41 

operation,  force  for 38 

-order  dispatching 340 

resistance 17 

components 17 

determination  of 22 

effect  of  curves  on 30 

of  winds 31 

on    energy    consump- 
tion   152 

on  power  consumption  127 

on  speed-time  curve . .  33 

formulae 23 

incidental 26 

motor-car 240 

spacing,  methods  of 339 

Transfers,  use  of 368 

Transformer    e.m.f.    of    single- 
phase  motor 60 

Transformers,  choice  of 327 

control  with 115 

Transmission  circuit 324 

development 324 

regulation 328 

types  of 324 

Transmission,  direct-current .  .  .  306 

high-tension 326 


Transmission  lines,  mechanical 

arrangement  of 329 

lines,  stress  in 329 

of  braking  forces 172 

potentials 327 

Transportation,  requirements  of  1 

Transverse  car  seats 209 

Triple  valve 191 

Trolley,  bow 227 

contact  signals 343 

overhead 279 

pantograph 228 

wheel 225 

wire,  grooved 287 

length 280 

methods  of  supporting.  .  284 

of  suspending 279 

stresses  in 281 

Truck  brake  rigging 182 

Trucks  and  running  gear 230 

bogie 232 

braking  of 174 

double - 232 

floating  bolster 232 

maximum  traction 233 

rigid  bolster 232 

single 230 

swinging  bolster 233 

swiveling 232 

Two-direction  signals 350 

Two-motor  equipments 144 

Types  of  transmission  circuits. .  324 


U 


Underground  conduit  system.. .  290 

Under-running  third-rail 289 

Uses  of  signals 335 


Vacuum  brake. 195 

Valve,  triple 191 

Variation  of  performance  in 

single-phase  motors. .  .  66 
Vector  diagram  for  single-phase 

motor . .  65 


390 


INDEX 


Velocity  grades 27 

Ventilation  of  motors 80 

Virtual  grades 27 


W 


Ward  Leonard  control 123 

Water  power 332 

rheostat 114 

Watt-hours  per  ton-mile 151 

Weakening  of  field  for  control. .  87 

of  motor  field  on  speed. ...  53 


Weight  distribution  of  electric 

motive  powers 9 

Welded  rail-bonds 294 

rail  joints 266 

Welsh,  J.W 104 

Werner,  G.  B 320 

Wheel  trolley 225 

Windage  of  motor 58 

Winds,  natural 31 

Wire  circuit  signals 342 

Wire,  trolley— see  Trolley  Wire .  287 

Wiring,  car 224 

Work,  mechanical 12 


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